Organize dialog presents server error message when removing resources

I keep getting this message when trying to remove a resource (in the organize dialog): "There was a problem accessing the server. Please try again."

I am mostly using ff3, but also tried in IE7 (using vista). Several times I've tried closing the browser and re-starting a new session. Sometimes it works 1 time, then goes back to the getting the same error message. Other times closing the browser does not help.

I can't figure out a logical pattern for why it is happening; sometimes it lets me remove resources, then for other resources I get stuck and receive the same message over and over. I've tried removing things one at a time, and also several items at once. I've also tried using different user accounts.