Found an issue with LM 2007 on Outlook 2010 on a recent deployment. The LM client (version from May 2011) is configured to use the Live Meeting Service from URL (such as https://www.livemeeting.com/cc/CompanyName). If the user’s Outlook profile is NOT configured to use cached exchange mode, then a scheduled live meeting gets an undeliverable message. If cached mode is off, a workaround is to change the “From:” field to use “Live Meeting Transport” instead of “Microsoft Exchange Server”.
Microsoft has confirmed this is a known issue, though I do not know if a KB has been publicly published.