When highlighting a program (or user) on the left hand side of the Session Browser, the Session tab on the the right hand side is not being populated i.e. there's just a blank display. This only seems to be happening on an 11gR2 database.
If v$session_connect_info does not have the following columns populated for a particular session id, then the session details will not be returned or displayed:
Uncheck the following from 'Visible Columns' on the left hand side (right click | Visible Columns) and on the right hand side (click 'show/hide columns' button, top left corner of Session tab data grid)
Waiting for fix in a future release of Toad for Oracle