Can't read ebook - format problem?

[nsxtasy]

I downloaded an ebook (in .epub format) from my public library, then used Adobe DigitalEditions to copy it to my Pandigital Novel eReader. I can see it on my bookshelf on the eReader, but when I try to open it, I get an error message:

Can't open book
The file format is not correct
E_OPEN_MISSING_EXT_GSTATE



TIA!