If the builder is running but failing, the following may describe the problem and its corresponding solution.
If the name of the Workbench project and the corresponding GNAT project file are not exactly the same, including letter casing, the builder will not invoke the Ada compiler and the overall build will fail. The content of the Build Console will look something like the following:
Note that the GNAT project file name and the name of the project inside that file must also be identical.