Just to get my head around building an AU I created an extremely simple gain patch. The building process is never successful however.
Duplicating the MyAU project and naming it MyGain works fine. When I build (before exporting the code) the result is a working product. But as soon as I try to build after exporting the code, the same errors keep occurring. These errors are reported in the MyGain.cpp file, which isn't actually touched with the code export. Below is an image showing the five errors (in lines 67, 92, 98, 98 and 150).
This is the patch: