Microsoft has just updated the following KB Article which includes a hotfix:
An update for the bootstrap certificate in System Center Configuration Manager 2007 Asset Intelligence is available
In Microsoft System Center Configuration Manager 2007, the issuing certificate that System Center Online uses to validate the bootstrap certificate expires in September 2012. After this date, System Center Online does not recognize the bootstrap certificate.
Note The current hardcoded Asset Intelligence (AI) bootstrap certificate is valid until June 19, 2015.