Can't join Custom Map games

[Shado]

Hi, I've been playing AC for about a week now, and I've played on all the regular maps. For some reason, when I join a custom map server, I can't spawn or even move around as a ghost? Maps such as Douze and Desert work because they're regular maps, but custom maps made by other players don't work for me;I can't spawn? I can chat, but right when I send the message it's gone. If you could help me, it would be great because I've been playing on regular maps, which get boring after a while.

Thanks,
Shado