I'm getting this error in the "Error Profiles" in Workspace with an InfoPath form integrated process.
Basically, the process is 5 approvals in series - the initial submission and the first review work correctly.
As reported in the Error Profiles section, "Second Review Activity" errors out with "The given key was not present in the dictionary"
Console Mode shows the following (among other uninteresting messages) when attempting to retry:
Outcome Evaluation: Started
Outcome Evaluation Result: Approve
Outcome Evaluation: Completed