I've been (trying) to learn astronomy, more specifically image reduction, using IRAF. I have, though, been having problems with the fits files from the Sloan Digital Sky Survey site. For example from this archive. I can't do anything with them. Implot, imstat all give errors. Using python, numdisplay can't work with this files either, although ds9 works fine. I assume that with IRAF everything is fine since it can work with .fits from other surveys. My insistence with the above archive is the availability of the files (I haven't been able to find other source of unprocessed files...) Can somebody help me? Is something wrong with the files or it might be something with IRAF?