[JimmXinu]

Originally Posted by sournamja

Here are some stories, the first one was on my previous Glo and opened just fine with it:

http://archiveofourown.org/works/2812721
http://archiveofourown.org/works/5442374
http://archiveofourown.org/works/5540198
http://archiveofourown.org/works/5457467

I guess I could go back to downloading everything manually, but you spoilt me with FFF

And thank you for the warning, I do realize the Kobo readers don't update stories - it's not a feature I use a lot, though, so it doesn't bother me.

Epubcheck doesn't find any errors in any of those, so we're left trying to figure out what Kobo might not like by trial and error.

First, Kobo might not like adobe-hyphenate: none; in CSS (this is included in FFF by default for older Nooks and isn't technically standard).

You can remove it by putting this in your personal.ini:

Spoiler:

[epub]
output_css: 
 body { background-color: #%(background_color)s;
        text-align: justify;
        margin: 2%%; }
 pre { font-size: x-small; }
 sml { font-size: small; }
 h1 { text-align: center; }
 h2 { text-align: center; }
 h3 { text-align: center; }
 h4 { text-align: center; }
 h5 { text-align: center; }
 h6 { text-align: center; }
 .CI {
     text-align:center;
     margin-top:0px;
     margin-bottom:0px;
     padding:0px;
     }
 .center   {text-align: center;}
 .cover    {text-align: center;}
 .full     {width: 100%%; }
 .quarter  {width: 25%%; }
 .smcap    {font-variant: small-caps;}
 .u        {text-decoration: underline;}
 .bold     {font-weight: bold;}
 .big { font-size: larger; }
 .small { font-size: smaller; }

Another possibility is that Kobo might not like <blockquote> tags. AO3 stories tend to use those around the summary description and author notes. You could test that by editing the epub and removing blockquote tags.

Just saving the epub from Calibre's Edit Book is worth trying, too, in case it's something obscure like Kobo caring about white space metadata files.

You might also try using Calibre's Convert feature and convert epub to epub. If that works on Kobo, we could compare and see what's different between the two.