Database upgrade from March 2013 to October 2013 Issue

Question

Hiya,
Am I missing something completely obvious trying to upgrade a March 2013 PU content database to a October 2013 CU and it's failing, using Mount-SPContentDatabase.
The farm account and my install user has the DB_Owner and SPDataAccess roles, however I still get the "schema versions does not match".
The March is Production and the Dev is October. The plan is to upgrade Production, atlas not right now now.
As far as I can see there is no CU requirements between March 2013 and October 2013?

Answer 1

1: Hard to get access to Production server right now.
2: Yes, however any custom components should not prevent the attach/upgrade. It might render the site unusable or create warnings in the upgrade process. But not prevent it.
3:
Microsoft.SharePoint.Upgrade.SPUpgradeException: This content database has a schema version which is not supported in this farm.     at Microsoft.SharePoint.Administration.SPContentDatabaseCollection.Add(SPContentDatabase database, Boolean
provision, Guid webApplicationLockId, Int32 addFlags)     at Microsoft.SharePoint.Administration.SPContentDatabaseCollection.Add(Guid newDatabaseId, String strDatabaseServer, String strDatabaseName, String strDatabaseUsername, String strDatabasePassword,
Int32 warningSiteCount, Int32 maximumSiteCount, Int32 status, Boolean provision, Guid lockId, Int32 addFlags)     at Microsoft.SharePoint.Administration.SPWebApplication.AddContentDatabase(SPWebApplication application, String strDatabaseServer,
String strDatabase, String strDatabaseUser, String strDataba...    916c6142-9501-42b6-a1e9-5d9418588008
...sePassword, Int32 cSiteWarning, Int32 cSiteLimit, Boolean bAssignDatabaseId, Int32 iAddFlags)     at Microsoft.SharePoint.PowerShell.SPCmdletNewContentDatabase.InternalProcessRecord()     at Microsoft.SharePoint.PowerShell.SPCmdlet.ProcessRecord()  
 916c6142-9501-42b6-a1e9-5d9418588008
Error Category: InvalidData    Target Object  Microsoft.SharePoint.PowerShell.SPCmdletMountContentDatabase  Details  NULL  RecommendedAction NULL    916c6142-9501-42b6-a1e9-5d9418588008