I recall we had this same issue or similar in 7.0. We deleted some users who were creators of some objects in Windchill, specifically workflow objects and that caused the workflow to stall. This is issue is exist in 8.0, but is resolved in 8.0 M050 going forward. Its being so long since I ran into this, but I seem to recall we found a way to reset the creator to the deleted user or some other user and that resolved it. If I ran across more information about this, I will certainly share it with you.
HTH,
Alexius C. Chukwuka
IT Analyst, PDP Systems
John Deere Power Systems
Product Engineering Center
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