I’m running WP 3.1.3 on an iMac. I was working on the admin page and noted the AddThis plug-in update notice. I used the automatic update and got a message that the plug-in had been updated successfully. I was asked if I wanted to return to WWp-admin and when I clicked that option the view just went blank. I could not log into WP-admin any longer and had to contact Bluehost and they reestablished the WP-admin log-in. We then tried to activate the 2.1.2 AddThis update and the whole problem repeated. I did get a fatal error message this one time.
I had to reactivate all of the plug-ins my site was using, but I would not activate AddThis. I note you’ve posted another update (2.2.0) but to tell you the truth I am very reluctant to even consider using it because I do not want to have to go through all this rigamaroll again. Were any changes made in 2.2.0 that would solve this problem? I note that many other users site essentially the same problem