If it's greyed out, the server is a different version of JJ2 than the one you're playing on. My guess is that you're using TSF to join 1.23 servers, which isn't normally allowed because your anims.j2a file would be different than the one you've got.

The solution? Either use Project Controller 4, or play 1.23, which is the version that is more commonly played online, for many reasons.

Oh, and this information is very commonly repeated in this forum, five minutes of searching would have given you the information you were looking for.