It might be because I'm still using an outdated version of mIRC (6.15 instead of 6.17). I have no idea if this is the cause, but I'll try it out soon.
However, when I do that, I'll have to load all of my old scripts back into the new version, which would be a lot of work in my case. Is there any way to automatically load all these scripts back without having to do this manually...