Hi Gary,
The same problem has been reported by some AstroArt users.
It seems that some versions of AstroArt write FITS files of the incorrect length.
A FITS file consists of one or more Header/Data Units (HDUs). Each HDU must be an exact multiple of 2880 bytes. Any unused space must be padded with blank or zero characters.
Verify that the length in bytes of the FITS file generated by AstroArt is an integer multiple of 2880. If this is not the case, then this is the reason of the PCL (Pleiades Class Library) error, and the problem is *not* a bug in PixInsight.
PixInsight relies on the CFITSIO library from the NASA/Goddard Space Flight Center for FITS support.
A possible solution might be editing the FITS file manually, with an hexadecimal byte-level editor, for example, to append the required number of blank chars to reach the correct size.
However, perhaps there is an update for the AstroArt application that fixes this problem.
Hope this helps. Please let me know.
Regards,
Juan