There are two recent threads in different forums complaining about search engine spiders from Microsoft.
A WebmasterWorld thread is specifically complaining about MSRbot, Microsoft's research bot, for attempting to crawl pages that don't exist. The other thread is from DigitalPoint Forums, which is just pointing out how busy MSNBot is on his particular forum.
The MSRbot is reportedly "asking for non-existent page" and the "URLs it supplied in UA string," can't be reach anywhere, said the WebmasterWorld member. Reportedly this has been an issue since back in April 2003 and is still going on today. It does not appear to be associated with the Live Search team, however.