Do 0.9 - note for packagers and source-builders
One of the build changes in Do 0.9 is that it will, by default, search for the dmcs (.NET 4.0-profile) compiler.
The .NET 4.0 profile and .NET 2.0 profile are not necessarily compatible. The latest do-plugins release (0.8.4) will default to using the gmcs (.NET 2.0) compiler, and will fail to build against Do 0.9.
The solution is to either build both do and do-plugins with dmcs, or both do and do-plugins with gmcs.