Robin,
I was able to reproduce what you were seeing with Maxim. If I don't calibrate the subs then they plate solve fine. After calibration, fewer image stars are found and the plate solve fails.
If I run the full version of Visual Pinpoint then it will solve both uncalibrated and calibrated files, but it does find fewer image stars in the calibrated files (e.g. 10485 uncalibrated, 8510 after callibration). The solve claims the FWHM in the uncalibrated file is 5.14 arcsec vs 4.88 arcsec in the calibrated file.
I can't see anything obviously wrong with the calibrated files. Most of the hot pixels are gone as is the vignetting, but that's expected
The overscan area looks pretty funky after calibration but cropping it off didn't make any difference.
That's as far as I've got so far. Something appears to be upsetting Pinpoint's star detection algorithm but I don't have any clues what it is yet.
I'll have a bit more of a play if I get a chance... Did you try new calibration files yet?
Cheers,
Rick.