You could try Windows MobiPocket Reader (or Creator). It will convert ePub to MOBI. Usually Calibre does a better job. Also, you might get different results using Calibre's command line options such as any2mobi. If you don't want MOBI, Calibre can then convert this to whatever you want.
If the ePub displays ok in Adobe Digital Editions and Calibre fails to convert it, then I suggest filing a bug report with Calibre. These typically get fixed very quickly.
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