How does a "clean install" contain 23 loaded scripts?
Any number of those 23 scripts could be the cause. Try with a *CLEAN* install of mIRC-- this means without any loaded scripts.
Alternatively you can unload scripts until the problem goes away (if it does)-- the last unloaded script would be the cause, at which point we can figure out if it's the script or some incompatibility between those commands and Windows7.