quickbooks error 6129
"https://qberror.com/quickbooks-error-6129/ is displayed when the database connection verification fails or QB attempts to access company files. The QuickBooks user is unable to open the company file as a result of the error. If there is a network problem in the network that the software is using, it will be unable to locate the computer or server that contains the file.

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William Acker commented
QuickBooks database server manager network diagnostics error is often encountered. Using QuickBooks in multi-user mode on a Windows server necessitates the use of a database server manager. This is how the storage server admin allows all applications on the network to view the business file stored on the server. QuickBooks can view the database server manager network diagnostics error for a variety of reasons.
https://qbtoolhub.com/quickbooks-database-server-manager-network-diagnostics-failed/