Probs with getting MU set up

Hi, I am trying to set up the multi user version and have hit a strange fault that I can’t find in any guide.
I input the required details in the install form and submitted. It didn’t go through at first and by checking on support here I managed to correct the problem by ftp.
Now there is a problem highlighted by Firefox which states:

Redirect Loop
Firefox has detected that the server is redirecting the request for this address in a way that will never complete.

Anyone know what this is please and how to correct it?
Thanks