You can bring back the side bars, on Pending Timesheets:
Click View Explorer and then click View Timesheet File Queue.
If you still cannot see them:
While Pending Timesheets tab is open click Options.
Click User Preferences:
Uncheck the Grid Customisation check box.
Uncheck the Toolbar Customisation check box.
Uncheck the ExplorerBarCustomisation check box.
Uncheck the Tab Customisation check box.
Click Save and Close.
Close the Pending Timesheets tab and reopen it.
The explorer bar should now be accessible.
