Experian messing up my life

I really hope someone will give me an explanation of why my credit score is so low, when all my accounts are up to date. None of them is in arrears. There's one more listing which is not updated as paid up, yet it is. I'm now trying to buy a house and the banks are giving me a hard time because of this. TransUnion has scored me highly, but Experian has listed me as a 5. I need to know why.