Any regular reasons about solving failure?

[zhongchun ji]

I have been working on the deep sky image solving these days. 

Most of my images were succeed, but some good files(with my eyes, I could see the stars. I thought they are good.)were still failed.

After explored the site: http://nova.astrometry.net/user_images?thumbnail_size=&sort=&failed=on , I found some of them (Total:193155) can be solved on my env.--CentOS 7 Mini.

So, with the same error message(likely):

[ 15976: 98.263] Field: /tmp/20180512.fits

[ 15976: 98.263] Warning: there was already a WCS file, and its timestamp has not changed.

solve-field.c:564:after_solved Failed to read WCS header from file /tmp/tmp.wcs.BcfyH5

 sip_qfits.c:267:read_header_file Failed to read FITS header from file "/tmp/tmp.wcs.BcfyH5" extension 0

 qfits:errfunc error: Failed to read FITS file "/tmp/tmp.wcs.BcfyH5"

Do really can not understand what happened. 

So, my question is -- in the past 7 years, did anyone got a conclusion -- regular reasons about why the solver failed?

Thanks a million!

[Dustin Lang]

This message: "Warning: there was already a WCS file, and its timestamp has not changed."

means that you were solving an image called, say, /tmp/20180512.fits, and there was already a file called /tmp/20180512.wcs .

If you want to post your image, we can look at it.  There are lots and lots of reasons why images can fail.

--dstn