No successor defined for event - 4.6c

[Rick Sample]

We have been live for 2 months and this is the first time I have seen
this error message.
I have a basic user decision step DECISION-PROCESS. All I have is
Approve and Reject options.
The user states he selected Approve. I looked at the RESULT in
container for this step and see no value.
I can not restart after error! The WF is hung in error status.
 
I am assuming I could just manually change the result container to 0001
and restart again but
wanted to bounce it off this list first. This Wf has been running fine
for two months.
 
Any clues would be helpful.
 
Thanks!