To find incorrect permission, you may run the following commands:
find /home/xxyyzz/public_html/* -type f -a -not -perm 644
find /home/xxyyzz/public_html/* -type d -a -not -perm 755
Please note the following points while working with SuPHP:
1. The php script that you are attempting to execute has permissions of no more than 755 - 644 will work just fine normally, this is not something that will need to be changed in most cases.
2. The permission of the directory that the script resides within is set to a maximum of 755. This also includes directories that the script would need to have access to also.
3. You shouldn't have a .htaccess file with php_values within it. They will cause a 500 Internal server error, when attempting to execute the script.
4. The php_values will need to be removed from your .htaccess file and a php.ini put in its place, containing the php directives as explained above.