Symptoms

we encountered an issue today across users that they get to see an error message as below:
24411 K2:Domaink2service from mIP]:]Port] is not allowed to open the worklist item with SN=XX_XX","anonymous"
 

Diagnoses

It seems this is related to impersonation and authentication issues .
Due to upgrade to 4.6.11 from k2 4.6.7 Check for custom implementation prior to k2 4.6.7.
 

Resolution
the analysis goes down to the very specific error related to the K2 engine (K2 Server service) sees incorrect user requesting the worklist item. This can only be possible by failure of impersonating the original user opening the form to the K2 service.

Another thing could be causing this is the way you open the worklist item – I couldn’t open the tasklist view as it was checked out to other users – but you are using the custom worklist broker which was built prior 4.6.7 with no-claims authentications in the picture while in 4.6.11 user authentication is purely claims-based. This I would suggest need further investigation if the problem arise again.