Nice and strange one this.
I've installed an SSL certificate on my site and am encouraging users to use SSL'd access to the forum (as it's harder for companies to block, keeps their cookies and requests secret, and prevents referer info being sent to third party sites).
Now when I surf on https:// , the 1.2 version fails. Yet when I surf http:// the 1.0 version works.
What I've done is to combine both.
If 1.2 works it uses it, otherwise it rolls over to the 1.0 version.
Strange, interesting... fixed