Mount-SPContentDatabase : This content database has a schema version which is not supported in this farm

Problem:

When you are trying to mount a SharePoint content Database and you got the error message "This content database has a schema version which is not supported in this farm." as seen below:

Mount-SPContentDatabase : This content database has a schema version which is not supported in this farm.
At line:1 char:1
+ Mount-SPContentDatabase "SharePoint_Site_DB" -DatabaseServer ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    + CategoryInfo          : InvalidData: (Microsoft.Share...ContentDatabase:
   SPCmdletMountContentDatabase) [Mount-SPContentDatabase], SPUpgradeException
    + FullyQualifiedErrorId : Microsoft.SharePoint.PowerShell.SPCmdletMountContentDatabase

Solution:

 The issue often occurs when you are trying to attach a content database to a SharePoint Server which has a different version level as the current one. For example the former content database was attached to a SharePoint server which was running SharePoint 2010 with SP1. But the current new server has only a fresh 2010 installation without SP1. To solve that upgrade your SharePoint 2010 Server to have the same Buildversion of the other SharePoint Server.

To know your SharePoint Buildversion, you can execute this command with the “SharePoint 2010 Management Shell”

 (get-spfarm).buildversion

and you should get the current buildversion:

Major  Minor  Build  Revision

-----  -----  -----  --------

14     0      6126   5000