I just created a really interesting problem.

I tried to add an optional field to the container in the list of invoices within a batch.

The error message is "Internal error:field [51] of [@i65ainv] is not a currency or number field"

There is an OK button but it just pops the same message again. Same result with trying to close or escape. When I shut down the program with Task manager and restart, as any user, with editing of container allowed or not, trying to open the same container gives the same message.
Program file QIWIN.INI has changed so I am going to try re-installing.