why can i use your cgi..?

i uploaded your 'recent 15 visitor' in my page..

and i give the permission 755 at hits.cgi

and 777 at hits.txt and 777 at counter.txt

at last, i give 777 at this whole directory

then i open the browser

type http://my page/cgi-bin/hits/hits.cgi

but it has 500 Internal Server Error...

why is it so..? i dunno

didn't i do anythin'?? tell me plz :)