I got an email from someone who couldn't compile GibberMonkey 0.1, after referencing spidermonkey-dotnet 0.2.0. GM code has undergone some changes since the 0.1 binary release. It and SM.NET 0.2 are in the process of being refactored to present a good API to the library user. Enough catchup. The latest code from TFS on both projects will compile together. To be specific, the GM changeset 9678 will compile against the development branch ($/spidermonkeydotnet/development/spidermonkey-dotnet) SM.NET changeset 21914. Also, if your a codeplex.com member you can simplify all this by joining the project and hitting the TFS and mapping these projects to your workspace.