If you want to get rid of obsolete entries in the folder drop-down menu of the “Map Network Drive” dialog, you’ll have to modify the Windows registry.
Open RegEdit.exe and go to the key
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Map Network Drive MRU.
The following screenshot was taken after I cleaned up; before, there were also entries named “b” and “c” with old paths in it.
Also, the value for MRUList read “cba” — the order in which the most recently used entries were displayed in the drop-down menu. After deleting the values “b” and “c” (and fixing a typo in the value of “a”), I then edited MRUList, so that it now only contained “a”.
PS: As a reminder, for scripting purposes, the command line equivalent comes in handy.
To connect a drive to a certain drive letter (in this case, persistently):
net use u: \\Server\Folder\Subfolder /persistent:yes
Respectively, to disconnect the drive again:
net use u: /delete