We just released a .NET Framework 2.0 CLR update that we recommend be applied to every Exchange 2007 server. It is more urgent to install this update on Client Access servers with multiple protocols, but we recommend installing the update on all Exchange 2007 servers.
We are also integrating this update in .NET Framework 2.0 SP1, but I don’t have any ETA for that release.
More information about this update can be found in the Microsoft Knowledge Base: http://support.microsoft.com/kb/942027/
You can download this hotfix from https://connect.microsoft.com/content/content.aspx?ContentID=3705&wa=wsignin1.0&siteid=210. We recommend that you make a full backup of the server before installing this update, and once again after successful installation of this update.