Regular expression

I copied an expression on the site www.regexlib.com

Thats the expression :

^(?=.*[0-9]+.*)(?=.*[a-zA-Z]+.*)[0-9a-zA-Z]{6,}$

So a password must contain at least one letter, at least one number, and be longer than six characters.

I tested on the site and it seems to work fine, but when I try it on my ASP.net page, something strange happens...

"aB1234" or "aB1234A" are not accepted, but "aB1234AB" is allright :confused: ? It's not even the number of characters, because "1234abcde" isn't accepted too ("1234abcdef" if OK) !

What's the problem ?

Nobody ?