I have two questions:
1. We found that in order for emails to work in Marketo Sales Insight, we have to delete any unused modules from the code in our email templates before publishing them, otherwise we get an error when trying to send a test or an email using Marketo Sales Insight for Salesforce. Does this happen to anyone else? Is there a workaround?
2. What could other reasons be for getting the "Your email body has HTML errors" message?
Email 2.0 may not work well with SFDC I suppose.
Could you show us more about when and where you get the error?
You may want to code these emails as Email 1.0 or just straight email html instead of fancy modules. You can still do that. I'm assuming in this case you are only using these emails for Salespeople.
I ran a couple of tests on various templates and had no such issue (although I found quite a few other. i'll write a post on this).
So it is probably linked to your template or to the html you inserted in the editable zones.
What template are you using?