Opinion by
Judge MacPhail,Jewish Employment and Vocational Service, Inc. (Petitioner) appeals the order of the Board of Claims (Board) relinquishing jurisdiction over a contract dispute between Petitioner and the Department of Public *583Welfare (DPW). The Board’s order was predicated upon the finding that Petitioner failed to file its claim within six months after it accrued, as required by Section 6 of the Board of Claims Act, Act of May 20, 1937, P. L. 728, as amended, 72 P.S. §4651-6.
Petitioner, a non-profit corporation, was approved by DPW to provide partial hospitalization services to eligible recipients in Petitioner’s medical assistance program. The Petitioner was then reimbursed by DPW for the medical services provided. The Board found that in order for clinic providers to be compensated for services, they first had to submit claims of the services performed to the County Assistance Offices (CAO). The CAO is then responsible for determining the eligibility of the recipients for whom claims were submitted and verifying the quantity of medical assistance received by the recipient from the clinic provider.1
If the CAO deemed the recipient to be eligible and within DPW’s limited amount, the approved invoices were forwarded to DPW for payment by the controller.2 In the instant case, the Petitioner submitted invoices to CAO in the amount of $331,656 for services provided from May 1, 1976 through January 31, 1980. Although none of the claims were rejected by CAO, DPW only reimbursed Petitioner in the amount of $303,266, the sum $28,390 less than the amount billed.
Petitioner then made various contacts with DPW in an effort to be reimbursed for the $28,390. DPW informed Petitioner by letters dated August 27, 1981 and October 2, 1981, that it would not pay the Petitioner’s claim for the $28,390, unless the Petitioner provided specification of the unpaid invoices. The Board *584that a clinic provider was obligated during the period 1976-1980 to attach a list of invoices, including each patients name and the amount billed, should that clinic provider desire a detailed explanation of those invoices submitted and paid. The Petitioner did not do this.
Further correspondence continued by letter, between DPW and Petitioner, until May 20, 1982 when DPW suggested in writing that Petitioner file a claim with the Board. On July 22, 1982, Petitioner filed a claim with the Board. The Board found Petitioners claim to be untimely because it was not filed within six months of August 27, 1981, when the claim accrued. Petitioners appeal to this Court followed.
The first issue raised by Petitioner is whether the Board erred in concluding that Petitioners claim was untimely filed.3 Section 6 of the Board of Claims Act states in pertinent part that “[t]he board shall have no power and exercise no jurisdiction over a claim asserted against the Commonwealth unless the claim shall have been filed within six months after it accrued.”
Petitioner contends that as of July 22, 1982 when it filed its claim with the Board, the statute of limitations had not yet expired. Petitioner avers that DPW did not conclusively reject Petitioners claim, because there was continuing correspondence until May 20, 1982. In Department of Revenue, Bureau of State Lotteries v. Irwin, 82 Pa. Commonwealth Ct. 266, 269, 475 A.2d 902, 905 (1984), this Court held that' “[a] claim accrues for purposes of suit in the Board of Claims when payment is due and is withheld by the Commonwealth.” (Citation omitted.) We find that the letters dated Au*585gust 27, 1981 and October 2, 1981 constitute affirmative denial of payment by DPW.
The body of the August 27, and October 20, 1981 letters read respectively as follows:
Thank you for your letter of July 29, 1981, concerning payment for services provided at the Work Adjustment Center, before the implementation of the Medical Assistance Management Information System (MAMIS).
As you are aware, we have made every effort to resolve the various billing problems of the Jewish Employment and Vocational Service. Dr. Sue Moyerman of my staff worked with the Office of Medical Assistance to obtain payment on outstanding invoices from the A.P. Orleans Center. Another of my assistants, Marian Bass, worked with the Bureau of Provider Relations in Medical Assistance to help resolve your payment problems under MAMIS. Staff in the Bureau of Provider Relations will continue to work with you to resolve any new problems which might arise under MAMIS.
The Comptrollers Office has carefully reviewed your records, and is unable to find any evidence of unpaid invoices from the Work Adjustment Center. You say in your letter that JEVS has also been unable to identify specific unpaid invoices. Without these invoices, I cannot authorize payment.
Of course, if you can at any future time identify any unpaid invoices, we will be happy to review them for payment.
Exhibit C-3, R.R. at 93a (emphasis added). The letter of October 2, 1981 reads as follows:
This is in response to your letter of September 17, 1981, to Secretary O’Bannon concerning payment for services provided at the Work Ad*586justment Center before the implementation of the Medical Assistance Management Information System (MAMIS).
As Secretary O’Bannon advised Mr. Brown-stein in her letter to him of August 27, 1981, our Comptrollers office has been unable to find evidence of unpaid invoices from the Work Adjustment Center. Since JEVS has also been unable to identify specific unpaid invoices, we are unable to authorize payment.
Exhibit C-5, R.R. at 90a (emphasis added).
In view of the record, there is sufficient evidence to determine that Petitioners claim, filed July 22, 1982, was untimely. DPW, through its letters dated August 27, 1981 and October 20, 1981, insisted that, unless Petitioner provided the specific unpaid invoices, it would not and could not authorize payment. As of August 1981, Petitioner knew that it could not provide DPW with information as to which specific invoices were unpaid, and that, without the specification, DPW would not pay Petitioners claim. Thus, in light of Irwin, the Petitioners claim accrued in August of 1981, when payment was due and was withheld by DPW.
Petitioner further argues that DPW should be es-topped from claiming the statute of limitations as a defense. In order for the doctrine of estoppel to apply, however, Petitioner would have to show that DPW exhibited acts constituting fraud or concealment.
In Department of Public Welfare v. U.E.C., 483 Pa. 503, 397 A.2d 779 (1979), the Court, citing Nesbitt v. Erie Coach Co., 416 Pa. 89, 92-93, 204 A.2d 473, 475 (1964), stated:
[I]f through fraud or concealment the defendant causes the plaintiff to relax his vigilance or deviate from his right of inquiry, the defendant is es-topped from invoking the bar of limitation of action. (citations omitted) The burden of proving *587the existence of such fraud or concealment is upon the asserting party by evidence that is clear, precise and convincing, (citations omitted) It is also well established that mere negotiations toward an amicable settlement afford no basis for an estoppel, nor. do mistakes, misunderstandings or lack of knowledge in themselves toll the running of the statute . . . (citations omitted).
Id. at-512-513, 397 A.2d 784.
Petitioner contends that it was misled by DPW when DPW implied that it had exhausted all possible avenues for locating the specific unpaid invoices, and further allegedly provided Petitioner with inaccurate information on how Petitioner could search DPWs archives for the documentation needed to support its claim. There is, however, no evidence that DPWs action caused Petitioner to relax its vigilance or deviate from its right to file a claim. It was not incumbent on DPW to make out Petitioners claim. That burden was Petitioners. The record shows that Petitioner had full knowledge that DPW would not pay its claim as of August 1981. Petitioner, moreover, admitted that it had been recommended by DPW (Ms. Marian Bass)4 that it file a claim with the Board, yet it neglected to do so. Finally, it appears that Petitioner had all of the necessary information upon which its claim to the Board was based iñ its possession at a time when .the claim could have been filed in a timely fashion, but it failed to do so.5
*588We are satisfied that this is not a situation where DPW misled Petitioner or misrepresented to Petitioner that it should not file its claim. Furthermore, there is nothing in DPWs conduct to suggest the “fraud or concealment” necessary to invoke an estoppel, as set forth in U.E.C.
We, therefore, conclude that Petitioners claim was not filed within six months after the claim accrued; that DPW was not estopped from claiming the statute of limitations as a defense; and, consequently, that the Board lacked jurisdiction over Petitioners untimely claim pursuant to Section 6 of the Board of Claims Act.
Order
The order of the Board of Claims in the above-captioned proceeding is affirmed.
DPW has a limit on the amount of partial hospitalization services that a recipient may receive in a year. N.T. at 12.
DPW never makes payment on any invoice which lacks certification of approval by the CAO.
Our scope of review of an order of the Board of Claims is limited to determining whether necessary factual findings are supported by substantial evidence and whether an error of law was committed. Commonwealth v. Rodehaugh, 102 Pa. Commonwealth Ct. 592, 519 A.2d 555 (1986).
In Petitioners letter date.d December 7, 1981 to Mr. Radke (of DPW), Petitioner stated that “Ms. Marian Bass of your office suggested to me that the best procedure might be to file with the Board of claims. . . Exhibit C-6, R. R. at 94a.
Petitioner’s witness testified that all of the invoices were in its possession to support the claim for $331,656, but Petitioner did not know which invoices had been paid and which were unpaid, since DPWs reimbursement checks did not reference specific injvoices.