Upgrading vCenter Server with Microsoft SQL database fails with the following error message: What could cause this error?

An incorrect or missing database name would produce a database-not-found or connection string error during the initial installer checks, not a compatibility mode failure mid-upgrade.

Incorrect ports would prevent the installer from establishing a TCP connection to SQL Server entirely, resulting in a connectivity timeout error well before any database-level compatibility checks occur.

vCenter Server's upgrade installer validates that the SQL Server database compatibility level matches the supported range for the vCenter version being installed. If the compatibility level is set too low - for example, to a deprecated SQL Server version level - the installer detects the mismatch and aborts the upgrade with a compatibility mode error, requiring the DBA to alter the database compatibility level before retrying.

Insufficient database permissions would cause an access denied or privilege error when the installer attempts to read or write schema objects, which is a distinctly different error message and failure mode than a compatibility level mismatch.