clee (Is that your name?),
I feel your pain. I had install problems with both 5.0.29 and 6.0.9. With 6 I got to exactly what you are describing, same error message, could not go back or forward. And yes, I was running as the administrator. It resulting in a lot of cursing and hair pulling. Eventually, I solved it. Here are a couple of things I learned. I don't know if they will help, but I offer them for you to try.
In the main AC folder there is a batch utility called registeritall. Double click to run it, and it will unregister, then re-register all the DLLs. If this is the problem as Bert suggests, it may help.
I had used an uninstaller that removed the AC data file,registry entries, and other files, and a registry cleaner at various points, and it turned out that they created problems by removing things that AC needed to install and run properly. If you can reverse your registry cleaning, it may restore the needed entries. It is nebulous in my mind now(as I have tried to forget the frustration),but it seems to me that with V6 it was a file that had .pf suffix (for prefetch) in it. After I restored that from my recycle bin, I was back in business. I really don't know what that is, but it did solve the problem, and allowed the install to proceed. Maybe this will mean something to the more technically savvy.
Forget about 6.0.9, go to 6.0.10, even thought it is technically a beta, it has less problems. Yes, it still has bugs, but nothing that is unmanageable in my use of it. It installed without any problems.
Good luck, don't give up.
