OK, I just learned by reading a lot of posts, that the scripts needs
(IMAGETYP, XBINNING, YBINNING, FILTER, EXPTIME)
So, I guess the MaximDL skyflats plugin does not add this information to the FITS header, and I need to add it manually. So, I need to look at the values and make sure I get them right...
Cheers,
M.