Is there a way to capture and display errors in a button script.  Problem is that when the script fails, it just doesn't do anything as if it never ran.  The reason why it failed would be immensely helpful.

Yes, call
     local inst=mc.mcGetInstance();  -- Omit this if you already have done this
    mc.mcCntlSetLastError( inst, "Your error message here" );

That will display a message in the Mach4 status/error line at the bottom of the window, and also in the "History".

Or you can use:

  mc.mcCntlLog(inst, "Your error message");

Which will add an entry to the Mach4 log (view it from the Diagnostics menu, select "Logger").

Disclaimer: I am not at a PC with the Mach API docs.  In the plug-in API, there are two additional parameters in the mcCntlLog() call, the file name and line number.  I don't know if they exist in the Lua version, or if they are optional.  I *think* you can pass NULL and zero for these if you don't want or need them, but I'm not sure.

  mc.mcCntlLog( inst, "Your error message", NULL, 0 );

Bob

Yes, but how do I capture the actual runtime error that caused to script to fail?