I just copy/pasted that code into a new epub and everything worked as expected. Are you sure you don't have the plugin set to process ALL files in the epub, and it's in fact, a different file that's causing it to barf?
I have no doubt you may have found some markup that makes the algorithm barf, but it shouldn't be the code you posted.
Are you sure you have the very-latest posted version of the plugin? Version 0.3.0, I believe?
If that's the only file in the epub (or the only file you've told the plugin to process), and you're still getting the error, please attach a copy of that exact epub (if you can) so I can take a look.