Symptoms
The error is occurring in the SmartForms integration wizard on a workflow.
Go to the configure item reference screen and select next, then I get the error:
Item with same key already exists
Diagnoses
Issue appeared in 4.6.9 and a clod fix was made available (ticket 87633).
Client is currently running 4.6.10.
Resolution
The fix did not make it into the original 4.6.10 installer.
However it has made it into the 4.6.10.2 release.
I downloaded the update installer from the portal site, installed it and now I do not get the error.