I had problems with windows as well. I was able to resolve this by installing the WAMP pack on the server and using it only for prosper while using IIS/etc. for everything else.
Install PHP 5 Apache MySQL on Windows : WampServer
It really seems like it's some minor incompatibility in prosper for IIS. Would be sweet to fix. Unfortunately I'm a .NET developer not a PHP guy.
Install PHP 5 Apache MySQL on Windows : WampServer
It really seems like it's some minor incompatibility in prosper for IIS. Would be sweet to fix. Unfortunately I'm a .NET developer not a PHP guy.