Checks if the SQL Server Express version on the secondary site is at least SQL Server 2008 R2 Service Pack 1 (version 10.51.2500.0). ...

Checks if the SQL Server Express version on the secondary site is at least SQL Server 2008 R2 Service Pack 1 (version 10.51.2500.0).  If Configuration Manager did not previously install SQL Server Express (existing instance is not CONFIGMGRSEC), then Setup skips this check.