Exception has been thrown by the target of an invocation

Hi All

I have tried to reconfirm a purchase order after changing the delivery date and i receive the following error message:

'Exception has been thrown by the target of an invocation'

This has happened now on at least 2 completely unrelated orders in the last few days.

Can anyone please shed some light on what this means or what could have caused the issue. If i try to click view accounting distributions then i receive also receive the error message below. I'm not sure if the 2 error messages are linked in any way?

Any help will be much appreciated