Error when uploading images: ‘Missing temporary Folder”

Hi,

I have a well functioning Aqua site. Everything seemed to work fine, but all of a sudden I get an error message when I try to upload media: “Missing Temporary Folder”. The image never shows up in the media overview part of the page.

The site is http://www.doulasophie.nl

Any idea how I can fix this?

Thanks,

Rogier