Will do thanks.
The issue is that we've deployed SEP out to a few thousand users and many PCs have ground to a halt. Through trial and error we've traced it to the Proactive Threat Protection, by disabling the scans the machines seem ok.
I'm suspecting it related to COH32.exe which was appearing multiple times, and we also had some machines with out of memory errors.
However, we've found this out ourselves whilst waiting for Symantec to call on what was supposed be a priority 1 issue.