Comodo Internet Security stops IE11 working

I have just had to uninstall CIS from a client’s computer after he complained that his default browser (Internet Explorer 11) wasn’t opening. After many hours troubleshooting IE and the Windows7 OS as a last resort I decided to run without any security. Disconnected from Internet, uninstalled CIS and geek Buddy, lo and behold everything started working again as it should.
Assumed the installation was corrupted, restarted machine and reinstalled CIS. Original fault returned instantly. Reluctantly installed a different AV/Firewall all now OK.
Strangely, Chrome, Comodo Dragon, Chromodo and Firefox were unaffected.
Hope this helps someone else.
For info, the machine was a Lenovo laptop with OEM Windows 7 Home Premium 64bit OS.