unable to delete a network drive in windows 7

Open the Start menu and enter regedit into the Search box and press enter. In the left side panel, locate the following key:

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\MountPoints2]

Under this key there will be several entries. You will be looking for entries that look like: ##SERVER#FOLDER (Where ##SERVER#FOLDER = \\Server\Folder)

Delete the offending entries and reboot.

Disclaimer:

Be careful editing the registry in this way. Manually editing the registry can cause system cause system instability is done inproperly. I take no responsibility for damage done to your system as a result of this answer. You have been warned.