Valérie Cothenet 

I got this error in the past, and the workaround was to do each of the above steps one by one. So in the Files View, select the file(s) you need to prepare, click on the Batch Task button on the ribbon and slect the following tasks in order:

Keep going until you finish. If there is a task still triggering errors, you may select one file at a time, and then run this task again, since there may be a file with issues.

If you still have issues, come back to this post and state the full version of your Trados Studio licence, the offending step and the error message.