Upon using the /run command:

/run J:\folder

Explorer.exe crashed with a dialog box left "titled" and saying:

"/idlist,:636:2700,J:\folder"
Windows cannot find '/idlist:636:2700,J:\folder'. Make sure you typed the name correctly, and then try again. To search for a file, click the Start button, and then click Search.

I'm sure i have had this happen before in previous versions also.
It seems to be a random occurrence, and am unsure how to reproduce it, i thought the '/idlist' might make sense to Khaled.
Altho a quick Google search on "/idlist" it comes up with 1.5 million results. But nothing specifically on the message i recieved.

(i have a screenshot but had no-where to upload it, hopefully the text is all thats necessary)

Do you get the same problem using Windows run command, located at Start - Run?
If so, then this is a Microsoft problem, not mIRC

If you'd like to upload the screenshot, the host I use is ImageShack. You don't need an account to host there, but if you create one (and it's free), then any pictures that you host will be stored in your account and you can make the pictures either private or public (on a picture by picture basis).