The previous way that CIS hooked into 64bit OS could be defeated by some malware. Enhanced protection mode resolves this. To select use the tick box in Advanced Settings ~ Security ~ Defense + ~ HIPS ~ Settings and reboot.
32 Bit systems
You can use either mode on 32 bit systems, though enhanced mode may be a little less stable. You may be able to use enhanced mode on 32 bit system to resolve conflicts with other security programs, including conflicts that stop security programs working properly. It may also resolve conflicts with other programs that hook deeply into the OS.
64 Bit systems
You should only switch enhanced mode off on 64 bit systems if it is causing problems. Your system will be more vulnerable to malware if you switch it off.