We've noticed that customers may experience Exchange services timeout or long wait times for services or application to start up. This problem occurs when a server has no internet access or occasionally when a server has limited internet access. The cause of this problem is likely related to a routine check of the Certificate Revocation List (CRL) for .NET assemblies. In this post, I will provide some details regarding how CRL check affects Exchange server services and applications and how some registry settings can contribute to the problem (and solution).
Read more at source: http://msexchangeteam.com/archive/2010/05/14/454877.aspx