The Cash Management Edit Register task is running in CM.

Exit the CM Edit Register, then attempt to record your payment in AP again.

Error: "Payment could not be written to disk" (AP broken distribution records)

Error: "Payment could not be written to disk" (AP check number has been previously used)

Error: "Payment could not be written to disk" (AP invoice is missing distribution information)

Error: "Payment could not be written to disk" (in AP Record Manual/Print Quick Checks)