The build of the .NET Framework that we recently released source for was 2.0.50727.1433, which was the VS2008/.NET 3.5 RTM build. A small change was made to the Framework after that, and this new version, 2.0.50727.1434, was then delivered to Windows Server 2008 and Windows Vista SP1.
Since the source and symbols have to exactly match what's running on a developer's machine, this meant that customers running these new OS releases lost the ability to access the Reference Source for the parts of the .NET Framework that we've released. The new symbols and source have now been deployed for the following:
The rest of the released source/symbols weren't updated.