Quickbooks error code 6129 occurs when you attempt to open a company file, but you are unable to do so due to a failed database connection verification. When QuickBooks encounters an error, you will be notified and instructed to close the program. It is most likely a network issue causing trouble locating the computer/server where the file is located.
Causes for QuickBooks Company File Error 6129:
QuickBooks error 6129 occurs when different computers in a multi-user environment are not updated to the latest release. An error could be caused by any discrepancy

 

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Quickbooks Error 6129- 8 Amazing Ways to Fix

If you have a networking issue on the system containing Quickbooks or Company file. Then, read the full article to have a complete guide of Quickbooks error 6129