So I got this pop up too but after reading all of your comments, I decided to go ahead and enter my password. I only got asked once. Afterwards, there was another pop up (as my computer was logging in) saying something about "Your mobileme idisk syncing has been disabled" and something about something being moved to the desktop. Haha sorry for the vagueness. I wish now that I had screen capped that...
Also, on my desktop I now have a folder called "Previous local iDisks" and inside are two files. One is called rika.six_iDisk-2011-08-24-063037.sparsebundle and the other is called rika.six_iDisk-2011-08-16-143742.sparsebundle.
I have no idea what any of this means. But. I hope it helps
