Interesting that you mention background processes. Alot of software seems to ask not only that all programmes should be closed before installing - some also ask that background processes such as any servers, anti-virus, firewall, etc be closed as well. I can't see why this would be necessary for mIRC as I have never had this installation problem though it may be worth a try for those having difficulty.
They can then either restart the closed processes or simply reboot.
