Some servers are running the tekkit 3.1.1 version and that uses tube stuff 49.1.1 and other servers are running the new tekkit 3.1.2 and that use tube stuff 49.1.2. Try to log back into the server and remember which tube stuff it requires and change your build for tekkit. 49.1.1 is tekkit 3.1.1 and 49.1.2 is tekkit 3.1.2