Define "it still doesn't work".
It has nothing to do with the regex if your code doesn't work, the error is somewhere on your side, as that regex works fine. Btw, you do know that it won't have any effect if you have an on text event in the same script file above it with matchtext *, right? As that one will consume all on text.
Your original question has been answered, we can't help you further with your script, as it's something specific on your side.
Note that the regex matchtext was only added in mIRC 6.1, and that there was a fix for it in 6.15