Yep that's right, the System Center Online Authentication Certificate for Asset Intelligence has expired, and you'll need to replace it to overcome the sync issues you are probably seeing right now :-)
http://blogs.technet.com/b/configmgrteam/archive/2011/05/17/announcement-update-your-system-center-online-authentication-certificate-for-asset-intelligence.aspx
If you do use this certificate, you should be all over this announcement ...
Read the complete post at http://wmug.co.uk/blogs/r0b/archive/2011/05/19/system-center-online-authentication-cert-for-ai-has-expired.aspx