I am getting this error at the top of all WordPress admin pages:

Error: the / folder does not exist. Please create this folder before uploading images to your WordPress posts and adding SlidePress galleries.

The existing slideshows are working fine, but when I try to edit one it shows that the XML Source is Manual Entry and the source field is blank.

What is going on? Why did I start getting the error and how do I fix it?

I am running WordPress 3.1.1 and SlidePress 1.4.7

Thanks