This is the message you see when you have a Google Apps served domain that does not support OAuth.
On that same Google page with the “Currently this single sign-in feature is disabled for the domain yourdomain.tld,” you should see a link that says one of three things: “Go back to SaneBox,” “Continue to SaneBox,” or “Back to website”. Click that link.
When you get back to SaneBox, there will be a link that says “OpenID authentication failed. Use password instead.” Click that.