Hello,
It is important to understand that SEP 12.1 RU2 MP1 is a maintainance patch and could be applied only over SEP 12.1 RU2.
Upgrading or migrating to Symantec Endpoint Protection 12.1.2100 (RU2 MP1)
http://www.symantec.com/docs/TECH204449
Migration paths
Symantec Endpoint Protection 12.1.2100.2093 (RU2 MP1) can migrate seamlessly over the following:
Symantec Endpoint Protection 12.1.2015.2015 (RU2)
In other words, the Migration path would be:
Older version than SEP 12.1 RU2 >> SEP 12.1 RU2 >> SEP 12.1 RU2 MP1
Hope that helps!!