We have often seen customer facing issues with "Unable to Process request" popup, the reason is due to session problem and to overcome couple of things needs to be checked.
1. If you have SSO enabled then check the SSO timeout.
2. Clarity has got its time out setting via Administration --> General Setting --> System Option --> Minutes Of Inactivity Until Logout
3. This Minutes Of Inactivity Until Logout must be set less than the time out set on your SSO (for example if your SSO time out is 15 minute then clarity timeout should be 14 minute)
4. if you naviagate to any portlet and you get this error, check for the list page which might be retrieving huge amount of data and its exceeding the timeout setting either on the SSO or Clarity.
5. If you don't have SSO and still get the error then check for browser timeout setting set by IT administrators and this timeout should be greater then clarity timeout and calrity timeout should be lesser than the browser timeout.
Once this pop up comes you will see errors in the app log like
ERROR 2013-11-19 10:50:17,674 [http-bio-90-exec-8] clarity.ui (clarity:user:712094124__EEAD9B7F-4E2F-4BCB-B6EF-0209BFBB8CA2:none) UI_MSG[:Tue Nov 19 15:13:42 UTC 0530 2013:OnError called--Client Side Exception