1. Uninstall eRequisitions via Add/Remove Programs
  2. Open IIS.
  3. Find the eRequisitions and BBWebClient Virtual Directories under the Web Sites section of IIS.
  4. Right-click and choose delete.
  5. Launch WebPurchasing/WebInvoicing again.
If the issue persists, uninstall The Financial Edge WebPortal via Add/Remove Programs and reinstall it.