What do you mean "it won't let you access"? It works perfectly for me, on all the cars I can remember the numbers of.
I'm sorry - when I read it again, that sounds rude. What I mean is: what happens, when you try to use it?
I have found that it can't give an answer if the car is no longer listed or is too new to have ever had an MoT, but otherwise comes up with the dates of each MoT, since about 2007, and the full wording of any advisories, or reasons for failure. It's past history, of course, but if you are thinking of buying the car, it does give useful info on what work has been done and - for recent stuff - allows you to check that it
has been done.