TeamCity server can't start after upgrading to 2026.2 when using MS SQL

Symptoms

1. TeamCity is configured to use Microsoft SQL Server for its database.
2. TeamCity is updated to 2026.2.
3. After the installation files are upgraded, the page with the following error is shown instead of the data upgrade page: Unexpected error when initializing MSSQL classes for optimized inserts. Consider switching it off with "teamcity.db.inParams.disableOptimizations=true"

Cause

The most likely cause is an outdated JDBC Driver version. JDBC drivers prior to 6.0 aren't compatible with the improvements added in TeamCity 2026.2.

If you encounter this error and your MSSQL JDBC driver is newer (12.4+), get in touch with the TeamCity support team and provide the teamcity-server.log and teamcity-startup.log.

Resolution

Using the latest JDBC driver version is recommended. The documentation provides instructions for installing a new JDBC driver.

As a workaround, teamcity.db.inParams.disableOptimizations=true internal property can be used.