AEM inbox is not loading workflow items

There are several workflows running on and suddenly all the Workflow items in the inbox are not loaded. I see below error in firebug [1]. I think some workflow might be corrupted or something else. But how can we fix this issue so that users can see the work items in their AEM inbox. Quick response would be more appreciated.

Note: Side kick is working as expected and users are able to complete workflow from sidekick when it is assigned them.

[1]:GET http://<host>/inbox/models.json?_dc=1431054685829

Thanks in Advance

Siva