Fix 0X00000BBF Print Monitor Error

If you're staring at 0X00000BBF, you're probably stuck with a non-functional printer and a vague error message. I've seen this on Windows 10 22H2 and Windows 11 23H2, usually after an interrupted driver install or a failed printer update. Let's skip the fluff and fix it.

The Direct Fix: Delete the Corrupt Monitor Registry Key

What's actually happening here is that Windows can't load a print monitor DLL — a small file that handles communication between the spooler and your printer. The DLL is either missing, corrupt, or has the wrong entry point functions. The registry holds a pointer to this DLL, and if that pointer is stale, you get 0X00000BBF.

Stop the print spooler. Open Command Prompt as Administrator and run:
```
net stop spooler
```

Open Registry Editor (regedit). Navigate to:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Print\Monitors

Look for subkeys that don't match standard Windows monitors. Standard keys are: BJ Language Monitor, Local Port, Standard TCP/IP Port, USB Monitor, WSD Port. Any other key — especially one named after your printer brand (e.g., Canon BJNP Monitor, HP JetDirect, Brother Status Monitor) — is the likely culprit.
Delete that offending key. Right-click it, choose Delete. Confirm.
Restart the spooler:
```
net start spooler
```
Try adding or printing. The error should be gone.

The reason step 3 works is that each monitor subkey contains a Driver value pointing to a DLL. When the spooler starts, it tries to load every monitor listed. If one DLL can't provide the expected functions (like OpenPort, ClosePort, StartDocPort), the spooler throws 0X00000BBF and refuses to load any further monitors. Deleting the key removes the failed load attempt entirely.

Why This Happens: Corrupt Printer Driver Installations

Most people hit this after uninstalling a printer driver but leaving the monitor registry key behind. The uninstaller of many printer drivers (Canon, HP, Epson, Brother) is lazy — it removes the driver files but forgets to clean the Monitors key. Or the driver installation got interrupted mid-way, leaving a partial key with no matching DLL.

I've also seen this caused by malware that replaces the monitor DLL to intercept print jobs. If you find a monitor key with an obviously suspicious DLL name (like mon.dll inside C:\Windows\System32\spool\drivers\x64\3), scan your machine with Defender or Malwarebytes.

Less Common Variations of the Same Issue

Case 1: All Standard Monitors Show Errors

If even Local Port or Standard TCP/IP Port are corrupted, you can't delete them — Windows needs them. The fix here is to restore them from a clean copy:

Copy the entire Monitors key from a working machine (same OS version). Export it as .reg.
On the broken machine, delete the Monitors key entirely.
Import the exported .reg file.
Restart the spooler.

If you don't have a second machine, run sfc /scannow and DISM /Online /Cleanup-Image /RestoreHealth before attempting this. I've seen corrupt system files affect the localspl.dll that loads all monitors.

Case 2: The Monitor Key Is Fine, but the DLL Is Missing

Sometimes the registry key exists and the Driver value looks correct, but the DLL path doesn't exist. Check the Driver value under the offending key — it will say something like canonmon.dll. Navigate to C:\Windows\System32\spool\drivers\x64\3 (or WOW64 for 32-bit drivers) and verify the file exists. If it doesn't, either reinstall the printer driver (not just the basic driver, but the full software suite that includes the monitor) or delete the key as above.

Case 3: The Error Appears in Event Viewer but Not at Print Time

If you get the error logged but printing still works, you can safely ignore it. The spooler recovered by skipping the bad monitor. But I'd still delete the offending key — it's one less thing to break later.

Prevention: Clean Driver Uninstalls

The root cause is always a sloppy driver removal. Here's the only way I recommend uninstalling printer drivers:

Open Print Management (printmanagement.msc).
Under Print Servers > [Your Computer] > Drivers, right-click the offending driver and select Delete.
Check the box Remove driver packages from the driver store.
After that, open regedit and manually delete the monitor key (as shown above).
Reboot.

Skip the manufacturer's uninstaller — half of them don't clean the Monitors key. Do it yourself. Takes 5 minutes, saves you an hour later.

TL;DR: The print monitor error 0X00000BBF is almost always a registry key pointing to a missing or corrupt DLL. Delete that key, restart the spooler. Don't reinstall drivers until you check this first.