upgrade SEC 5.0 to 5.1 with error "Invalid source version: 50"

Whilst attempting to upgrade a server to SEC 5.1, I bumped into the error stating: "The Server cannot be upgraded, the database needs to be upgraded first." ..

Looking at Sophos KB article 65420 and running “UpgradeDB.exe –debug –sourceVersion=50” it comes back with an error:

C:\Program Files (x86)\Sophos\Enterprise Console>UpgradeDB.exe -debug -sourceVer
sion=50
27.09.2012 11:45:46      ... successfully completed.
27.09.2012 11:45:46 Validating parameter values ...
27.09.2012 11:45:46 Invalid source version: 50
27.09.2012 11:45:46 Exit code 1 (Invalid command line qualifier.)

In our case the regkey for the database server is pointing to the right location, albeit not the same server where SEC runs on.

Value Name: DatabaseConnectionMS
Value Data: Provider=SQLOLEDB;Integrated Security=SSPI;Initial Catalog=SOPHOS50;Data Source=SQLSERVERNAME;

I've opened a case with Sophos [#3474860] and will update this thread with future steps.