Strange error "Exceeding the limit" pop up when i click the action button for a newly entered standa

I have created a standard AP invoice, and matched to a PO.

It status now is "Never Validated";
When i click the action button , I get a pop error message "Exceeding the limit"

Then click OK and nothing happens ,

Please assist where to check as we are unable to do any transactions on this invoice ?

Is there a way for example to UN-MATCH this invoice from the PO , so it becomes un-matched, and PO Billed Quantity is reduced to 0.