GNAT GPS Could not determine target to build - ada

Question

I'm struggling with a custom project file that will build and execute, but I get this set of warnings (or errors, I'm not sure). After a Clean All and then when I click the Build -> Project -> Build All to bring up the Build All dialog box:
[2015-01-22 23:30:39] Could not determine the target to build.
[2015-01-22 23:30:39] Could not expand argument in command line: %T
[2015-01-22 23:30:39] Build command not launched.
These show up (in red text) in the Messages window before I click Execute to begin the build. When I click Execute, the build completes successfully and the program runs.
The Build All dialog has this in the options dialog:
%builder %eL -P%PP %X -k -s -d
What does this mean and why is it doing this?
If it would help, here is the project file:
project LogBuffer01 is
for Source_Dirs use ("src", "src\utilities");
for Object_Dir use "obj";
for Exec_Dir use "exe";
for Main use ("abt_log_buffer_main_b.ada");
package Naming is
for Spec_Suffix ("ada") use "_s.ada";
for Body_Suffix ("ada") use "_b.ada";
for Spec ("abt_mirror_specs") use "abt_mirror_specs_s.ada";
for Spec ("abt_log_buffer_types") use "abt_log_buffer_types_s.ada";
for Spec ("abt_log_buffer") use "abt_log_buffer_s.ada";
for Body ("abt_log_buffer") use "abt_log_buffer_b.ada";
for Spec ("abt_log_buffer_rom_acess") use "abt_log_buffer_rom_access_s.ada";
for Body ("abt_log_buffer_rom_acess") use "abt_log_buffer_rom_access_b.ada";
for Spec ("screen_output") use "screen_output_s.ada";
for Body ("screen_output") use "screen_output_b.ada";
end Naming;
package Pretty_Printer is
for Default_Switches ("ada") use ("-i5");
end Pretty_Printer;
package Compiler is
for Default_Switches ("ada") use ("-gnat83");
end Compiler;
package Builder is
for Default_Switches ("ada") use ("");
end Builder;
package Check is
for Default_Switches ("ada") use ("-d");
end Check;
end LogBuffer01;

Answer 1

The meanings for the builder are defined here. There's no point in me translating your command string, suffice to say that %builder translates to gnatmake because you only compile Ada. gnatmake's switches are described here.
BTW, I have this for package Builder:
for Default_Switches ("ada") use ("-g", "-C", "-s");
but in another properly-working project I have
for Default_Switches ("ada") use ();