We recently installed V2R1 in MS2012 server and facing this issue in web client after logged in .
SSP Error Log:
Im not sure if you have installed Update 3 Fix Pack 1 for V2R1 yet but if not i would recommend you try this as there have been many fixes that you will benefit from and will likely correct the issue you are experiencing. If after upgrading you are still encountering an issue we would recommend you submit a case to our Support Team via the Support Center with the time of the error occurrence along with your Hopex error log files. We will then be able to investigate this issue further for you.
Are you looking to leverage UAS for authentication? If not, or as a test, I would recommend setting the "DelegatedLogin" key to "0" in the "web.config" of the "hopex" site (by default, C:\inetpub\wwwroot\HOPEX).
Try the above after committing the change and restarting IIS and the Hopex Srevices:
I hope that helps.