Drive problem??

Almost certainly not PE. A kick to the mount, wind, mirror flop or a bad gear wheel, motor or similar. Mirror flop is probably the answer if you hear no weird noises or crunching from the gears/motors.

If your mount is on soft ground and you were waliking around it, that may also be an issue.

HTH

Dave

You'd definitively get some sort of mirror flop if you crossed the meridan during the exposure, it doesnt look like PE to me

One thing to keep in mind is to make sure the last motion of the drive is to the west, if you pan east and settle on the object the drive has to stop and change direction and if you dont leave it enough time before theat and the exposure, your gears can actually go backwards and cause all kinds of weird errors before it settles.