Using info in apt bug #351056, I cleared my problem. Sorry for the extra noise. Maybe someone could move this report to apt, and merge with the above bug.
In my case, it was enough to delete some stale files from /var/cache/apt/archives. I only had this problem with libselinux1 and libbonobo2-0. I guess those two got upgraded at exactly the wrong time for the amd64 transition to official Debian servers. -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]