narrowing down the suspects...
Well, if you're certain you could blind scan without this problem in the past...
... and you've done a full factory reset of the receiver...
... one has to wonder about your dish, LNB, motor, and where it's mounted.
Have you added any new equipment?
Maybe an in-line amp? If so, maybe it's overloading.
What is the dish?
What LNB?
What is your motor mounted on?
The idea of being slightly out of alignment is a reasonable alternative, if it's not the receiver.
How long have you had the receiver?
Has it been subjected to any trauma?
Perhaps a 2-year old and a cup of orange juice?
edit: oh, here we go...
I was looking through your old posts for a clue....
Did a blind scan on AMC5 (79W) and for some reason while it was scanning, the receiver said "moving satellite dish" and then upon completion of the scan, it moved the dish to AMC6 (72W) and to GBN, which it seemed to pick up while scanning AMC5 (79W). I'm using a Fortec Mercury II receiver. Anyone else experience this and/or know why this would occur? About two weeks ago I did a master reset on the receiver because I had transponder overload.