ISSUE
There may be times where you encounter a situation in KTA where you are unable to restart a Job at a desired queue and may receive an error such as "INTERNAL ERROR".
RESOLUTION
In one case, this was due to the documents being deleted as the job was in an On-Hold status for longer than the configured retention settings. Upon investigation with the Repository Object Browser, the Document IDs were not found due to deletion. This situation is one of the things to be aware of in KTA when configuring the Document Retention settings. The retention time set for documents will delete any documents past the set date whether the jobs that contain the documents are completed/finished or not.
To avoid this issue, please make sure that your retention time is configured to a period longer than the longest time a job will be active.