In answer to your second question ("what troubleshooting techniques...?), you should insert "writeln" statements in your code, so you can see the values being set and the what code is being run.

In general, you probably want to reserve the Global Code space for variable, subroutine, and function declarations that are used by two or more other events.

To debug this, fill this routine and the routines using these variables up with writeln statements. You should also try populating your list element with hard-coded values, so you can see if the problem is in the  routine that gets the data from the engine, or the routine that puts it in the list element. You might also call @error/@errortype/@errorstring between built-in functions to see if the last function failed -- displaying the error with writeln.