If there is an abortable SYNTAX error in the script, then the script cannot be run/debugged. You will hear a beep from the computer speaker. The Debugger Window will pop open and display an error message indicating why the SYNTAX condition was raised along with the ANSI error number. The editor window (for that script) will jump to the line where the error occurred and place a red arrow next to it. You may wish to use the Check script for errors command first to make sure that your script contains no abortable errors in it prior to debugging.
Note: Only one editor at a time can be run. You must use the Halt script command (or the Abort debugger command) to first stop any running script before you try to run another editor's contents as a REXX script.
You can also start the debugger silently running in the background by using the Debug -> Run command. This differs from the "Start debugger" command in that the script is not initially paused at the first instruction. Rather, the script initially runs until the next breakpoint or Break command.