QuickBooks Error 6123 0: What It Means and How to Fix It (2026)
Quick Answer
Error 6123, 0 means the company file is open in single-user mode on another computer and cannot be accessed for multi-user mode until that user switches or closes the file.
What Error 6123, 0 Actually Means
Error 6123, 0 is a mode conflict error. Someone has the company file open in single-user mode, which locks it to that one workstation. Other users trying to access it get Error 6123 until the first user either closes the file or switches to multi-user mode.
Common causes:
- Another user has the file open in single-user mode
- A previous QuickBooks session did not close properly, leaving a phantom lock
- A QuickBooks process is running in the background on another machine
- The file was opened by double-clicking (which defaults to single-user) rather than through the QuickBooks application
How to Fix Error 6123, 0
Ask all users to close QuickBooks
Have everyone on the network close QuickBooks completely. Check Task Manager on each computer for lingering QBW32.exe or qbupdate.exe processes and end them.
Switch to multi-user mode
On the server (host computer), open the file and go to File > Switch to Multi-User Mode. This allows other workstations to connect.
Delete the .LCK file
In the folder with your .QBW file, look for a .QBW.LCK file. This is the lock file. If no one has QuickBooks open, delete this file. It will be recreated when someone opens the file properly.
Restart QuickBooks Database Server Manager
On the server, restart the QBDBMgrN service. This clears any stale connections and allows fresh multi-user sessions.
Why Error 6123, 0 Keeps Coming Back
Error 6123 recurs when users open the file by double-clicking it (which opens in single-user mode) instead of opening QuickBooks first and then opening the file (which respects multi-user settings). Train users to always open QuickBooks first, then use File > Open.
Scan Your QuickBooks for Error 6123, 0 Conditions
Hubricon's Data Janitor scans your QuickBooks file and flags the exact conditions that cause Error 6123, 0 — uncategorized transactions, duplicate entries, reconciliation gaps, and more. Free scan, no signup required.
Takes ~90 seconds. Read-only access. We never modify your QuickBooks data.
Frequently Asked Questions
How do I tell who has the file open?
In QuickBooks, go to File > Utilities > Display Users. On the server, you can also check the Windows file sharing session to see which computers have the file open.
Can I force someone out of the file?
The QuickBooks admin can close another user session from Company > Set Up Users and Passwords > Set Up Users > View Users. However, this may cause unsaved changes to be lost.
Is it safe to delete the .LCK file?
Only if you are certain no one has QuickBooks open. The .LCK file prevents data corruption from simultaneous writes. Deleting it while someone is working can cause data issues.
Why does this happen every Monday morning?
Someone likely left QuickBooks open over the weekend in single-user mode, or the server had a scheduled restart that did not properly close the QuickBooks session. Set up automatic logout policies.
Does Hubricon cause file locking issues?
No. Hubricon accesses data through the QuickBooks API, which is read-only and does not interfere with file locking or multi-user access at all.
Stop fixing QuickBooks errors manually
Hubricon monitors your QuickBooks data 24/7 and prevents the conditions that cause errors like 6123, 0. Connect in 2 clicks, see results in 90 seconds.