I've created a custom template and tested it with a test campaign. When I try and use my custom template as an autoresponder template, I get this error message:
"Sorry, we've run into a problem converting your old template to our new templating language"
I used their example template as a framework, so I use the same header info (doctype, html tag, mata tag...)
EDIT: It looks like its only when I add existing templates. If I add a template through the autoresponder prompt I don't get an error message.
It sounds like there could be something wrong on the backend with the template. Would you contact support with your account information and let us know which autoresponder and which template? We can take a look. It's already the weekend in Sydney (where our offices are) so it might be a couple of days until one of our developers can fix the issue (if they're needed) but one of our support team will get back to you ASAP and at least see if anything can be done in the meantime.
It sounds like you found a work around as well.