There is a business rule in KFS that prohibits users from creating Requisitions (REQS) on an expired account. If you receive this message, check first to ensure that the purchase is allocable to the correct account and that the expiration date is correct.
If you're using a Contracts & Grants account, has the project been extended? If the project is continuing, confirm that an extension has been requested of the sponsor and, if so, edit the account to remove the expiration date. If the account has truly expired, purchasing supplies is not expected to occur.