As Iori implied, it'd be simpler, easier and more sensible to use the mIRC AVoice feature - although I thought if you were using 'isin' you'd have *RJ|*!*@* on your AVoice list ;p
For the benefit of edumacation however, your code should work fine. However, firstly you might like to use on @*:join:#RJ2K3:{ as this means it'll only activate when you're an op (Which is of course the only time you can voice someone, bar non-default modes such as half-op).
The most likely reason it doesn't work though is conflicting code. Put the code in a new file, in Remotes (ALT+R, and File > New). Also make sure Remotes are on with /remote on.
Regards,