ShowDialog supports a full range of error codes. If you pass an incorrect number of parameters or if some of your parameter values are inappropriate, ShowDialog will exit gracefully with a beep without displaying a dialog. If you find this happening, debug your script with the line:
"put the result"
immediately following the line containing the call to ShowDialog. This will load the error message into the message box. These messages should be fully understandable.
If you find that your dialog appears at a spot on the screen and then immediately jumps to the position that you specified in the parameter list (or jumps to center itself) it is because you neglected to UNCHECK the "visible" checkbox on the DLOG template.
Also, for dialogs that have a title bar, remember that these dialogs must NOT have a go away box! Be sure to UNCHECK the "GoAwayFlag" checkbox on the DLOG template.