Originally Posted by mikelv
Thanks for your feedback! Could you send me a link to the ePub-file (if it's free)?
Unfortunately some webservers are not configured the right way, so they don't send the right mime-type for ePub-files. The result is, that EPUBReader doesn't recognize that it is ePub-file which you to try to open and doesn't process it. I have already fixed this in a new version which I'm testing in the moment.
P.S. In the meantime you could just download the file to your disk and open it in Firefox via "File/File open".
It wasn't on a server. I was doing File-->Open.