mbstring

I am using php 5.2 with mysql 5 and I would like to initiate mbstring with gd2 for use with webasyst. I have added c:\php to windows path and in the php.ini the session_mbstring and session_gd is activated. the php_gd2.dll is in the right place. But when I let the webasyst install script check, I get the answer that there is no mbstring and no gd support installed. Anny ideas? Thanks in advance.