Sorry, back again with this problem.
This happens in sales and purchases when trying to “process” an order.
Background: I took the wrong decision not to choose the standard German SKR04 account scheme, but trying to enhance the “minimal account table”. Bad idea, but now such it is. Due to advice of an accountant, I had to rearrange some of the accounts. Now this problem occurs again. I checked all the accounts, not of them is closed. Definitively not.
Is there any possibility for solving this problem - or will I really have to start over from close to scratch with SKR04?