how are you running the script ?
the failsafe would be to use a simple php.ini with NO extensions to start off with, make a batch file (or type at dos ~)
and in your script dl() the exact path (or set the simple_php.ini extension directory to point here)
c:/path/to/php.exe -q -c c:/path/to/simple_php.ini -f c:/path/to/gtk_scripts.php
note that existing php-gtk will not work with php5 or php<(I think)4.2
... if you are using this , http://www.firepages.org/gtkdev.htm then I have had several comments that the file associations don't work , all I can say is they have always done for me , at least on 2k/XP