I guess I missed this part of your post:
when logged in, the URL shows: http://m.slapp.me/checklogin.php it should be http://m.slapp.me/login_success.php as there is a redirect
Looks like it's getting a script error.
Turn on PHP error reporting and see if you can get an answer to what it is.
This is what I get when I try to login:
There's a mistake somewhere, I can't see it.