When do you get this error? On start? When you try to use agents?
You realize Windows 7 is not yet released, and an OS cannot be judged by what's in a pre-release (not even the official beta). MS Agent might in fact be included in W7. Until it is released, there is no forum for this discussion indeed.
If not, this is still not a bug. If Microsoft removes agents from the OS it makes sense that mIRC would be unable to use them-- neither mIRC or the OS would need an update, we would just need to deal with no more agents. AFAIK though, the solution is simply to download and install MS Agent on your own, from: http://www.microsoft.com/msagent/