Search script problem.....cannot open inv_index file

i installed the script and I ran into two problems:
1. When I go to the search_form.html to enter my password and index my site, it says server 500 error and it isnt even a script! Can you help me see what is wrong??
 
2. If I call search.pl from the browser...it says error. withe following comment:  Cannot open /home/alqazwin/public_html/cgi-bin/search/data/inv_index: No such file or directory at search.pl line 83.
There is no inv_index file!!! 
Why does it says that and how can I fix that???
My script is at http://alqazwini.org/cgi-bin/search4/search.pl


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