E_PACK_ERROR message when uploading ePub files

Does this happen to just one particular book? Have you tried uploading another and still get this error?

If you're uploading a PDF file, ensure sure it has no encryption on it. Our system will automatically encrypt your document with military grade algorithms immediately following upload.

Adobe's DRM scheme is a little stringent on the formatting of ePub files. Even documents that go through epubcheck can get stuck during the encryption phase though that is a very rare case. We'll dig through our server logs to see if we can produce some actionable items for you to get these up and running.

In the meantime, please run the file through the epubcheck tool found at https://code.google.com/p/epubcheck/ Its output could also be helpful in identifying the problem.