error pass create user mobile

Hi everyone, after googled around two days, I decided to create a discussion here. I don't know if anyone can noticed this problem. I'm trying to use poster add-on in firefox to create a user in drupal. The parameters are user:test, pass:test, mail:test@test.com. After I post it, drupal created a user called test, BUT! the tricky thing is I can't login by using the username and the pass which I just created. Anyone knows why? My guess is that I config something bad, or miss-installed something. The article I followed is https://drupal.org/node/790416. Thank you, any idea would be nice.