I rebuilt my laptop recently with Windows 7 and installed AppFabric, .net4, VS 2010, etc. 

 When I came to configure BIzTalk 2009 I got the error in the subject line because the SSOSQL assembly needed to be re-registered. 

Follow the instructions here to get it to work http://tomas-simonavicius.blogspot.com/2010/02/sso-service-failed-to-start-after.html