I suspect your Preferences have Clean Source set to Pretty Print. Try changing to Pretty Print Tidy, and the tidy part may fix the doctype on load.
I think we need to make sure the default is Pretty Print Tidy for 0.6.0 users that are set to Pretty Print to handle cases like this. But even so, it may also be necessary to automatically clean up the DOCTYPE provided by Book View when just using Pretty Print or when Clean Source is OFF.
Oh, the error is, I think, saying it expected whitespace after the EN" but instead it found >.