Recently I ran into an issue with my Windows 7 desktop in that it would no longer allow me to use my favorite theme, Bing Dynamic. I could access, “Personalize Desktop”, select the Bing Dynamic theme and even go into settings and select the shuffle checkbox, change time, etc. However, every time I selected Save Changes, it reverted back to a solid color background. Since I enjoy viewing the desktop photos throughout the day, I was pretty disappointed and began searching for answers.
I initially came across this post that recommended deleting the RSS feed and re-downloading it. I tried that but it did not fix the issue. After more searching to include several changes to my search terms, I finally hit gold with the following search string; “select themeserver desktop background doesn’t work”.
I followed the steps in the article and now have Bing Dynamic working again 
In the event you would like to learn more about Dynamic Feeds, here is a link to Frequently Asked Questions. I hope this saves you some time in the event you run into this issue.
