9.03 is the only version I've run in to the issue of not being able to log in. I unpacked the distribution file and copied it to 2 locations on the server. On one, I changed the database_connection.asp file to reflect the location of my v9 database (which was upgraded from v8), and the other I didn't change it so it used the "stock" database.
I told my server to give me read/write/delete/modify permission for the stock one (no need to do for the v9 database in my secure database folder, as the whole folder is already setup for this).
Tried using default username and password on the stock install, and it reports the invalid username or password error. Tried logging in on the other install using my upgraded database, and the same problem.
This worked fine with 9.02 and below.
I also tried taking a 9.02 install and replacing the files noted as changed for the 9.03 install, and as soon as I replace the global_variables.asp file, the forums crash reporting redefined variables.