Trying to fix 'warning: no compiler specified for language "Ada", ignoring all its sources'

[Ben Hocking <benjaminhocking@gmail.com>]

I've gone through the gems 68 and 69 here:
http://www.adacore.com/adaanswers/gems/gem-68/
http://www.adacore.com/adaanswers/gems/gem-69/

I was able to reproduce the examiner/simply/POGS results, but if I actually try to compile the code from GPS, I get the message:
  gprbuild -d -P/Users/Dependable/Tools/Spark1/search/default.gpr
  default.gpr:1:09: warning: no compiler specified for language "Ada", ignoring all its sources
  gprbuild: no sources to compile
Similarly, if I try to compile just search.adb, I get:
  gprbuild -ws -c -u -P/Users/Dependable/Tools/Spark1/search/default.gpr search.adb
  gprbuild: "search.adb" is not a source of any project

If I go to Project->Edit Project Properties, I see that Ada is checked as a language, and its compiler is set as gnatmake. The file default.gpr looks like:
====
project Default is

--   for Languages use ("Ada");

   package Ide is
      for Default_Switches ("examiner") use ("-index_file=search.idx", "-config=search.cfg", "-flow_analysis=data", "-vcg");
--      for Compiler_Command ("ada") use "gnatmake";
   end Ide;

   package Compiler is
      for Default_Switches ("ada") use ("-g", "-O2");
   end Compiler;

end Default;
====
With the lines commented out with "--" having no impact whether they are commented out or not (since these are the default values).

I'm using the native gnat toolchain, version GPL 2011 (20110419), and my GPS version is GPS 5.0.1 (20110113) hosted on x86_64-apple-darwin10.2.0. I'm on OS X 10.6.8. I was able to compile in GPS a couple days ago, so I feel like something's changed (although I haven't updated any software since then), but I have no idea what.

Any help would be appreciated.

Thanks,
-Ben