Found something helpful today I forgot to document the last time I encountered it.
When you install the Xigla LiveSupport component into an AC7 website, you have to make a change to the primary web.config file. There's a tag that has to be modified.
Edit the ~/Web.Config file in the root of your AC7 store. Search for the word "theme" – should take you right to a tag <pages theme="AbleCommerce" …>. Remove the theme="AbleCommerce" portion BUT LEAVE THE REST.
Save it. Now you'll be able to hit the LiveSupport start URL without the error "Using themed css files requires a header control".