How to create an XML in an absolute path with WWW Class

Hi, I have been reading all questions and posts around here but I still can't get my stuff to work.

I'm interested in creating (from scratch, or if already created delete the existing one and creating a new one) a XML file to an absolute path (aka server). It has to be using WWW class because I'm highly interested in Web Player export. I know how to serialize and deserialize my data correctly, but I just don't understand how to upload it. I might think you need some kind of php file to create it or change some writting permissions, but I don't know anything about those.

I tried all kind of stuff but I always arrive to the "Error submitting XML: necessary data rewind wasn't possible" error.

If someone could help me out it would be great ! It has been a lot of days failing already....

Thank you for your time,

Best regards.