I had a similar problem but it was with the 'password.php' script of Chapter 9. Larry's reply pointed me to the saved values and I found that 'root' and 'root' were being saved for the localhost URL (ref. Safari->Preferences->Passwords). I deleted just that one Preferences item and got the script to work.
However, that raised for me the question of how this particular script's FORM became associated with the remembered values. When I was first trying to prevent 'root' from being populated as a value in the first (email address) field of password's FORM I tried a couple of things, including giving that input field a name other than 'email'. Nothing I tried worked, until I physically deleted the item in Preferences.
So, what causes a particular form item to be associated with the saved values, and why was this NOT happening with the relative-same fields in the register script?
And, also, is there a was to specify that the form NOT populate from those browser-saved values?