Hi noc,
As per my understanding, the definiton issue is with Windows Server 2008 R2 client (SEP client) and not on SEPM.
You can try with "Rx4DefsSEP" utility to remove the corrupted defs on the client. Be aware that running this will remove all the defs stored on the client machine. After running this tool you can manually run liveupdate or it will automatically get the defs as per the LU policy configuration.
You can get this tool by contacting Support. More information about this tool can be found in the below link,
http://www.symantec.com/docs/TECH93036
Hope that helps.