You were concatenating a PHP variable to 2 undefined contants, which PHP assumed to have a value the same as their names (an assumption I wish PHP did not make and instead threw an error/exception instead of just a warning).
"Please give us a simple answer, so that we don't have to think, because if we think, we might find answers that don't fit the way we want the world to be."
~ Terry Pratchett in Nation
Thanks for your answer, but it still gave me the same error.
So I tried something else now, and it gives me a different error, but it waits about 5 seconds before it gives the error, before that it is just a blank page.
now the error is:
Warning: mysql_connect() [function.mysql-connect]: Lost connection to MySQL server at 'reading initial communication packet', system error: 110 in /home/www/wearecrunch.dk/gammelsjuf/ajax/register-process.php on line 60