Symptoms

Customer was getting this error when trying to look at instances in workspace for two different workflows. One of which is not used and the other is used frequently.

Error: Could not load the grid: Failed to return Process Instance Data Table: Object reference not set to an instance of an object.

I have worklist instances I cannot action or delete related to the workflow that is not used.
 

Diagnoses

Using the Process Version Migration Utility from K2 Community, http://community.k2.com/t5/K2-blackpearl/Process-Version-Migration-Utility/ba-p/73689_
We were able to see that some of the instances of the problem have the version set to 0.
 

Resolution

Customer was able to modify the process by placing a Place Holder event at the end of the workflow and redeploy then using the Process Migration Utility to migrate all instances to the newly added activity. All instances were able to complete, and the instance page was able to load as expected.