Windows ME should be perfectly compatible with mIRC, so I would assume it's something the script does. Choosing a script over using new, less buggy and non-exploitable software is not a good idea, there are plenty other FISH scripts in the sea
(See this page
for some script-related links).
It is possible to use a script to do it, see this thread
. This is not recommended, you should drop the script and get the latest version of mIRC.