I ran into the same exact problem today. I started by renaming the mu-plugin directory by adding a 1 in front and nothing. Then I remembered the last plugin I installed was backwpup (back up plugin). I added a 1 to the directory and I’m back to normal. The weird thing was that the backup plugin was updating 3 to 4 times a day. I thought it was due to the changes I was doing. But even when I was just checking out each site? Never ran into problems with my HTML and Flash Sites. Bummer.
