I had this problem too, with version 7.43. I had 7.19 installed before that, and I installed 7.43 to a different directory without uninstalling 7.19 and without doing a portable install. Context menus wouldn't pop up when right-clicking on nicks, either in the channel or in the nicks list. They also stopped working for 7.19 after installing 7.43, where they had previously worked.
I did what you said and installed 7.43 in My Documents in portable mode, and now for that installation context menus work.
