All Trek has continuity problems, as King Daniel
points out. Enterprise
's are no worse than those of any prior series or movie. It's just that it covers a period that we had decades to build up assumptions and expectations about. Most of the things that people saw as "continuity errors" in ENT were really contradictions of their preconceptions and beliefs about the 22nd century, rather than any actual canonical information.
Really, it would've been a total waste if all ENT had done was confirm our existing assumptions about the era. That would've been boring and pointless. It's good to be surprised.