Make sure you are running HIPS Extension 7.0.4 or later on your ePO server (7.0.4 is required for Win7 support). 7.0.5 is the latest extension.
Thank you Kary. I checked the ePO server and we had extension 7.03 installed. I've now downloaded and applied the 7.05 extension and all is fine.
Installing this latest extension also sorted the system tray icon