[Update @ 4/11/2014, 12:30 PST]
We believe we've isolated the issue to a specific name resolution server - the issue has been isolated and mitigated, and you should now see full mitigation.
We're aware of an issue where roslyn.codeplex.com may fail to resolve. We're actively working on it, and will provide updates via this blog post.
The MSDN Service Delivery Team