QuickBooks Error 6129, 0 is a common error that occurs when trying to open a company file in QuickBooks or when creating a new company file. It indicates that QuickBooks was unable to access the company file due to various reasons. Here are some possible solutions to fix QuickBooks Error 6129, 0:

Update QuickBooks: Make sure you are using the latest version of QuickBooks. If not, update your QuickBooks to the latest release as the error may have been fixed in the newer version.

Run QuickBooks File Doctor: QuickBooks File Doctor is a diagnostic tool provided by Intuit that can help in resolving common QuickBooks file-related errors. You can download and run QuickBooks File Doctor from the Intuit website to diagnose and fix issues with your company file.

Disable antivirus and firewall temporarily: Antivirus software or firewall settings can sometimes block QuickBooks from accessing the company file, resulting in error 6129, 0. Temporarily disable your antivirus and firewall settings and try opening or creating the company file again. Remember to re-enable them after resolving the error.

Move the company file to a different location: If the company file is stored on a network drive or external storage, try moving it to a local folder on your computer and then try opening it in QuickBooks. Sometimes, network or external storage issues can trigger this error.

Manually resolve the error: If none of the above solutions work, you can try manually resolving the error. You can create a new folder on your computer, copy the company file to the new folder, and then set up Windows permissions to allow QuickBooks to access the file. You may also need to rename the company file to resolve any issues related to file name or extension.

Restore a backup: If you have a backup of the company file, you can try restoring it to a new location and then opening it in QuickBooks.

Regards,
Peter