Release System Hold Errors

We're trying to validate a series of Payables invoices which have a system hold on them that the Invoice is not matched to a PO. We'd like to be able to release the hold with a reason of "Workflow Process Release" but instead receive an error stating that "You cannot manually release this type of hold. Resolve the hold condition and resubmit the invoice for validation (AP-810056)." In researching this error, I have not found much information on how to successfully release these hold conditions. Has anyone come across this before and had a solution?