Start | Run | Type regedit, and click OK. Expand the ShellNoRoam Key in order to expose the subkeys...under the following Registry branch:
HKEY_CURRENT_USER | Software | Microsoft | Windows | ShellNoRoam | BagMRU
HKEY_CURRENT_USER | Software | Microsoft | Windows | ShellNoRoam | Bags
...and delete the BagMRU and Bags subkeys (in the LH pane). Make sure to back up/export the two Keys before deleting them, then reboot. Deleting the two subkeys resets all your folder settings to their defaults. If the above doesn't work for you...copy the following into Notepad, and save it with a .reg extension:
-----------------------------------------------------------------
Windows Registry Editor Version 5.00
[-HKEY_CURRENT_USER\Software\Microsoft\Windows\ShellNoRoam\BagMRU]
[-HKEY_CURRENT_USER\Software\Microsoft\Windows\ShellNoRoam\Bags]
[HKEY_CURRENT_USER\Software\Microsoft\Windows\Shell]
"BagMRU Size"=dword:00001f40
[HKEY_CURRENT_USER\Software\Microsoft\Windows\ShellNoRoam]
"BagMRU Size"=dword:00001f40
[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer]
"NoSaveSettings"=dword:00000000
------------------------------------------------------------------
Windows remembers 400 folder settings, and when that number is reached some settings aren't retained any longer...the above Registry edit increases that number to 8000. After saving the above with a .reg extension, double-click the Registry file in order to merge it into the Registry...and make sure to reboot after making the above changes.
Edit: There shouldn't be any spaces in ShellNoRoam or CurrentVersion. The formatting on the forum incorrectly puts spaces in those two Registry entries, so make sure to edit them in Notepad before merging the .reg file.