I agree Ringil's answer, and I wanna add some inner meaning.
try to feel following sentence
我们中间有奸细。 : There is a spy among us(/There are spies among us). (but not me.....)
我们中间有坏人。 : There is a jerk among us(/There are bad guys among us). (but not me......)
我们之间有障碍。 : There are (mental) obstacles between us.(You and me)
我们之间没有爱。 : There is no love between us.(You and me)
朋友之间要互相帮助。: One must help your friends when he's facing some difficulties.(I agree, and I will do this)
so when you are trying to express some information that you will emotionally and subjectively agree with, we often use "之间".
when you are trying to express some truely existed, objective and you strongly confirmed (after inferentially considering), we may use "中间".
Try to feel the atmosphere when you are talking, if you wanna be closer to the person you are talking with, use " " which one? if you can answer it, I think you may understand what I want to explain..
Hope it will help you...cheers.