When the Open Object Rexx scripting engine is run in the so-called sandbox mode, access to some system and REXX resources is not allowed. You can find some examples here (click on the script text (colored in blue) to run it):
Accessing the filesystem:
call lineout 'c:\temp\illegal.tmp', 'File I/O is not allowed!'
Issuing host commands:
'date /t'
Creating STREAM objects:
test = .stream~new('c:\temp\illegal.tmp')
Accessing certain entries in .LOCAL:
say .local['OUTPUT']