Interesting. That sounds like your password validation is failing. Does your user have a password defined? You can check this with passwd at the command line. The other thing you might check is the UID / GID of your user (with id). I believe by default, RSP requires UID to be greater than 1000?
Some other things to check are whether your user has a home directory that is owned / readable / writable by the user. That would not be throwing an invalid user / pass error, though.
Another route you might take is to use the pamtester utility that comes bundled with RSP to ensure that the PAM authentication is happening appropriately.