Before I had this problem I was removing libraries from Calibres library list that no longer existed. I have a copy of my library sent to dropbox everyday and I may have opened that library in Calibre instead of my regular one when I was done, but I don't see how that could have emptied it. I gave the libraries different names but that didn't help because the name in dropbox now is the name I used to use for my regular library.
I think I'll change the name to include the word dropbox so I don't get confused again.
Unfortunately I deleted the epub files from my Tab S, but I have a mobi on my Nexus I downloaded from the content server around the same time. This mobi caused Moon+ to crash and AlReader gave an error when trying to read it. The mobi is 724 bytes and when I opened it as a text file this is what it contains:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"></meta>
<title>404 Not Found</title>
<style type="text/css">
#powered_by {
margin-top: 20px;
border-top: 2px solid black;
font-style: italic;
}
#traceback {
color: red;
}
</style>
</head>
<body>
<h2>404 Not Found</h2>
<p>book: 7236 does not have format: MOBI</p>
<pre id="traceback"></pre>
<div id="powered_by">
<span>Powered by <a href="http://www.cherrypy.org">CherryPy 3.2.2</a></span>
</div>
</body>
</html>