Downgrade to Roslyn 0.6.4033103

Uninstall-Package Microsoft.CodeAnalysis
Manually remove packages from packages.config
and references from the .csproj
Install-Package Microsoft.CodeAnalysis -Version 0.6.4033103-beta -Pre
Simulate unsuccessful downgrade

Suppose during the downgrade not all versions of referenced assemblies
were updated. For example, some other package was dependent on
Microsoft.Bcl.Metadata and even though you're using Roslyn 0.6, you're
using Microsoft.Bcl.Metadata 1.0.11 which was brought by Roslyn 0.7.
This causes an exception