I know what the problem is...
There are 2 main versions of JJ2, The Secret Files (1.24) and plain, normal Jazz Jackrabbit 2 (1.23).

Most players are on 1.23, and the two versions are incompatible (you cannot join 1.23 games using TSF, and 1.23 users cannot join TSF games). To play in the greyed out/transparent servers, you need to get 1.23 somewhere (if it isn't 1.23 or 1.24, then download the 1.23 patch). You can also use Project Controller and change your version number. Download here: http://www.jazz2online.com/J2Ov2/dow...p?levelID=1334
Then open JJ2, open Controller, go to Tools, Change version, and finally choose '1.21, 1.22, 1.23 - Full (1.21)' and click 'Change!' You should then be able to join the greyed out servers, but not 1.24 games.

Also, 1.23 and 1.24 have animations that don't quite match, so everyone else will look really weird in the game, but don't worry about that.