The following errors are logged in the K2 Hostserver and Windows Event viewer logs:
"[FQN]:[domain]\[username] does not have permissions to open the process"
A process will be started successfully, and within the K2 Product you will not see any errors. This will happen even though the relevant user can open or start the process. However, if you look at the K2 Hostserver and Windows Event viewer logs, you will notice the error messages.
This was identified as a bug in the product. It has been fixed in the May Cumulative Update Fix Pack 9 Update: http://help.k2.com/kb001954