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?