suddenly today unable to process partial refunds

I have made partial refunds without problem for years with from zen cart via paypal until today.

I have not changed anything but when trying to process a partial refund today I got the following error:

There was a problem refunding the transaction amount specified. (Transaction failed due to internal error) 10001

zen cart v1.3.9h, usd payment.

Any help would be appreciated.

10001 "internal error" is a problem on PayPal's end.

Log a support ticket with them: www.paypal.com/mts

Will do.