"Object reference not set to an instance of an object"

Hi, when trying to generate the target translation I now often get the error message "Object reference not set to an instance of an object". I had a computer breakdown, used my laptop where the problem started, but now installed Trados 2015 new on the new machine, but the problem persists. Packages seem to work, first I thought it only happens with xliff files, but now also with an Excel file.

Any ideas what the problem might be?