whats a windows php thing. Your error reporting is set way too high so its reporting an empty variable. Try editing index.php and remove this if you can not turn down error reporting as its merely a safety check
Double check there are tons of threads here your vblicense number is entered correct in your config-inc.php file and you can verify your cookie settings in photopost by viewing the settings table settings 171-173 and make sure they are set the same as vb. You can rerun install again and input the proper info if needed and are not familar with phpmyadmin.