The global repository user (generally "dm_bof_registry") will have been set to inactive in the global repository. This will have occurred due to the global repository password details in the "dfc.properties" file being incorrect on one or more of your servers within the environment.
Obtain the correct encrypted password for the global repository user and ensure it is correct on each server "dfc.properties" in your environment
Login to the global repository and set the user back to active
You should now be able to view the Documentum Inbox without issue