The PDE Build actually uses the Eclipse compiler. What I don't know for sure is how project specific settings are being used. E.g the access rules are written into a file javaCompiler...args which you can find in ${buildDirectory}/plugins/<yourplugin> along with the generated build.xml file. The build.xml file also contains the properties javacSource and javacTarget. I guess they are read from the project's settings if the exist but I am not sure. However, you can set it globally from the pluginbuilder editor's Properties tab. I guess your build problems vanish if you set javaSource and javacTarget to 1.6. or 1.5.