Melanie,
The information you gave is not enough to allow someone to help you.
The supposed error message
"Restore must be resumed prior to first image expiration on 17.04.2005..."
Is not an error message.
It is just a reminder that if you want to "resume" the restore job then you must do it before the image expires on April 17.
That is normal when you cancel a job.
If the restore seems to just stop and not do anything, then I suggest checking for a pending mount request. I would also check to see if the requested media is in use or even in the library. Again that should produce a pending mount request.