Fix ERROR_ALREADY_ASSIGNED (0X00000055) in Windows

When does this error show up?

You're trying to map a network drive — say Z: to \\server\share — and Windows throws ERROR_ALREADY_ASSIGNED (0X00000055). The message reads: "The local device name is already in use." It happens most often after a reboot, a VPN disconnect, or when a USB drive that was using that letter gets yanked out. The drive letter looks free in File Explorer, but the system still has a stale record of it.

What's actually going on?

Windows keeps a hidden list of drive letter assignments — both persistent (survive reboots) and temporary (session-only). When a network drive disconnects uncleanly, or you remove a USB drive without safely ejecting it, the letter stays reserved in the background. Next time you try to map it, the system says "nope, that letter's already claimed" even though you can't see it anywhere. The culprit here is almost always a leftover persistent mapping from a previous session.

Fix it: Remove the stale mapping

1. Open a command prompt as administrator — hit Start, type cmd, right-click, and pick "Run as administrator."
2. Run this command to see all current mappings:
   

   net use

   
   Look for your drive letter in the list. If it's there, you'll see it with status "OK" or "Unavailable."
3. Delete the mapping for that specific drive letter. Replace Z: with your letter:
   

   net use Z: /delete

   
   If it asks for confirmation, type Y and hit Enter.
4. Now remap the drive cleanly:
   

   net use Z: \\server\share

   
   Or use the persistent flag if you want it to survive reboots:
   

   net use Z: \\server\share /persistent:yes

5. Test it — run dir Z: and you should see the files.

If the delete command fails or the letter isn't listed

Sometimes net use doesn't show the stale mapping. Windows Registry holds a separate list. Here's the nuclear option:

1. Open Regedit — press Win+R, type regedit, and hit Enter.
2. Navigate to:
   

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

3. Look for a subkey named after the drive letter, like Z:. Right-click and delete it.
4. Also check this location for network drive leftovers:
   

   HKEY_CURRENT_USER\Network

   
   Delete the subkey matching the drive letter.
5. Close Regedit and reboot. Then map the drive again.

What if it still fails?

Two things to check after the registry cleanup:

• Check physical devices — Open Disk Management (diskmgmt.msc). Look for any USB or external drive that might be using that letter. If you see it, right-click and change the drive letter to something else.
• Check Group Policy — In some corporate environments, IT locks drive letters via Group Policy. Run gpresult /h result.html and open the HTML file. Look under "Administrative Templates" > "System" > "Drive Mapping" for any restrictions.

If you've done all that and the error still pops up, the issue is likely on the server side — maybe the share name changed, permissions got revoked, or the server itself is down. Verify the path manually from another machine to rule that out.

That's it. 90% of the time, a single net use /delete nukes the problem. Don't waste time rebooting or reinstalling network drivers — it's never that.