The code snippet
call lineout copies('x',999)
will crash the interpreter (REXX-ooRexx_4.1.2(MT) 6.03 28 Aug 2012, 64 Bit, Windows 7)
Thanks to Mark Miesfeld here's the initial output from the debugger:
"A buffer overrun has occurred in rexx.exe which has corrupted the
program's internal state. Press Break to debug the program or Continue
to terminate the program."