Bob,
Is there any chance that you made changes to the MPCORB database or the calculations that take it for use it in ACP?
I cannot center asteroids anymore. When I type "MP Concordia" into the SingleImage web form and get coordinates, the values in the RA Dec boxes say "emphemeris." And that's right. However, the computed coordinates as posted in the log are off in RA by about 8 or 9 arcminutes (34 seconds of time) to the west. There's a very small error in declination, a couple arcsec, as well. This puts the target outside of my smallish FOV. The image is centered at the requested, incorrect coordinates.
When I put an NGC object in the Target Name window and get coordinates, and then take an image, the target is dead center, and not displaced in any direction. NGC uses a different database.
I had the same result when I tried to image MP Europa (the minor planet) - the telescope pointed too far to the west nominally by the same 8-9 arcminutes.
I don't recall this being a problem in the past, though it's been a long time since I've visited asteroids. I wonder if others have noticed this.
EDIT: Just another point about the data.
Starry Night Pro shows the asteroids as well. I could see there the FOV I actually captured, which was west of the asteroid's real position, and when I manually moved the telescope to the position described by SNP, Concordia and Europa were imaged in their correct position against the correct FOV.