Symptoms
we face a problem in a move event, where we move an InfoPath form (it can be any file type) into a folder in a SharePoint library.
The following error is logged in error profiles for the process instance:
"Server was unable to process request, ...andgt object reference not set to an instance of an object"
Diagnoses
The behavior is reproducible by creating a workflow that moves/copy a document into a folder on the same document library.
Resolution
This has been logged as a bug for 4.6.10 and 4.6.11 and a coldfix is available through K2 support.