The user defined form is pretty messy and it could be a number of things wrong. I would just remove the xml validation from the page (it could still be valid html as xml is much stricter). You can do this via removing the <?xml header from the Page.ss file.
Thank you alot willr for your quick answer, it works now, half, it shows some Notice tags before the page starts, and makes it look a little messed up, but the files are still only read and write for the user, so the client can't watch them without i'm going to set permissions new. Is there a solution for this too?