Symptoms
When trying to access SmartForms in K2 Designer a Server Error was being thrown:
The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040
Diagnoses
The error itself was indicative of a mismatched assembly(s) vs the current version of K2.
Resolution
Running repairs against both the SmartForms and the control pack resolved this issue.