Symantec Endpoint Protection (SEP) 14 is using a new scan engine called SDS which stands for Static Data Scanner. Prior to SEP 14, the engine used for virus scan is running in the kernel mode, however SDS runs in user mode level.
While the 14 SDS JDB definition files can be accepted by SEP 12.1 client when dropped in the inbox (%ALLUSERSPROFILE%\Symantec\Symantec Endpoint Protection\CurrentVersion\inbox) and by Symantec Endpoint Protection Manager 12.1, they are considered incompatible.
Forcibly using the 14 SDS JDB files on SEP 12.1 clients may cause high network congestion between server and client or client may turn into unusable state.
Forcibly using the SEP 14 SDS JDB files on SEP 12.1 clients may cause high network congestion between server and client or client may turn into unusable state.
Use the appropriate JDB definition file for SEP 12.1 client, see the Security Response link and look where it specifies the JDB files specifically for 12.1: