I've just installed a new MS Intellimouse Explorer 4.0 on my PC, and for some reason, the scroll wheel won't function in mIRC. I can roll that wheel all day long, and there's no scrolling in the channel windows.

When I use my old mouse (an older version Intellimouse Explorer), it works fine. I've installed the drivers and software for the new mouse, and scrolling works perfectly in other applications.

Other details:
OS - Windows Vista Business
mIRC - v. 6.21

Is this (another) Vista compatibility issue? Just a MS issue? Anyone encouter anything like this?

not using vista, but just a question.
does your scroll wheel function in other programs that use it, such as notepad, internet explorer, excel - or is it just mIRC having the problem?

It works in everything else I've tried so far: Mozilla Firefox, Internet Explorer, foobar2000, Windows Mail, and Adobe Acrobat. So far, the only program that will not scroll is mIRC.

Edit: Uninstalling the Intellipoint 6.1 software that came with the mouse seems to have resolved the issue. The "generic" drivers with Vista seem to work fine. I'll leave it as-is for now, but if anyone can think of another solution, please post.

Sounds like incompatible drivers/software in Vista, which isn't too surprising. Wait for a newer version of the drivers/software and try again.