Ok, apparantly our server hasn't updated the Protocol from 47 - 48. Protocol 48 is a new update which stops players being able to russian walk (for those who don't know, russian walking is binding your "crouch" to the "mouse wheel" which not only makes the player harder to hit but gives the player "silent running").
As it stands, there is nothing we can do about the update. Apparantly all we have to do is restart the server but as we've tried this about 15 times I doubt that is the problem. I have been intouch with TeamHost who are the company which supply the server to us, all we can do now is wait for them to do somthing about it. I'll update the informations as soon as I have more.