Fix ERROR_NOT_JOINED 0x00000088 on Drive Joins

Yeah, this error's annoying. You're in Disk Management or using a script, trying to clean up mount points, and Windows throws ERROR_NOT_JOINED (0x00000088) — The system tried to delete the JOIN of a drive that is not joined. It means exactly what it says: the drive or folder was never properly joined, or the join got orphaned.

The Fast Fix

Open Command Prompt as Administrator. Then run:

mountvol [drive: or path] /d

Replace [drive: or path] with the actual drive letter or folder path. For example, if you're getting the error on drive X:\, run:

mountvol X: /d

That usually deletes the stale mount point. If it still complains, add the /p flag to remove the mount point and dismount the volume:

mountvol X: /p

Had a client last month whose backup software left a ghost junction on drive R: after a failed restore. mountvol R: /d killed it in seconds.

Why This Works

Windows stores drive mount points in the registry under HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices. When you assign a drive letter or path, it writes a junction. If that junction gets corrupted — say, after a disk failure, a RAID controller swap, or a quick format — the reference stays but the target volume is gone. mountvol /d cleanly removes the registry entry without trying to touch the missing volume. Disk Management's GUI sometimes trips over itself trying to validate the target before deletion, but the command line doesn't care.

Less Common Variations

1. Junction Point on a Folder

If the error happens on a folder path like C:\Mount\Data, use:

mountvol C:\Mount\Data /l

That lists the volume GUID. Then remove it with:

mountvol C:\Mount\Data /d

Or, if the folder's empty, just delete it in Explorer — Windows will clean the orphaned junction.

2. Stuck Drive Letter After Disk Removal

Pulled a hot-swap drive without dismounting it first? The drive letter lingers. If mountvol doesn't work, boot into Safe Mode and run Diskpart:

diskpart
list volume
select volume X
clean

But be careful — clean wipes the volume's partition table. Use it only if the disk is dead or empty.

3. RAID Controller Failover Left Orphans

Seen this on Dell PowerEdge servers with PERC controllers after a drive rebuild. The new drive gets a different bus number, so old mount points break. Run mountvol /r to re-scan all mount points and remove stale ones automatically. Doesn't always work, but worth a shot before manual cleanup.

Prevention

• Always use Disk Management's "Change Drive Letter and Paths" dialog to remove joins — never manually delete the folder or registry keys.
• Before yanking a drive, dismount it first: right-click in Disk Management, choose Offline, then remove.
• If you script drive operations, include a check: mountvol [drive:] /l to verify the join exists before attempting deletion.
• Back up HKLM\SYSTEM\MountedDevices before any disk surgery. It's tiny, but saves hours if something goes wrong.

Bottom line: mountvol /d is your friend. Skip the GUI for this one — it'll just frustrate you.