Are you talking about not being able to right-click users (ie. right-click and do whois, kick etc...), or something else?
If the former, I too am having that problem. I am currently using mIRC v6.15. I have it installed on two different machines and both have the same problem.
I didn't notice that a new version is available (6.16) and if that is the fix, I will try it. Would just like to know what is wrong with what I have. I will also mention that I haven't registered the program yet, but have talked with some friends online and they said that that shouldn't matter.
TIA for any help.