"cannot execute external command" message ...

Hi, on one machine, I am encountering following message - something like: cannot execute external command message ... when I use 'call/shell I tried to use call/shell instead of simple 'call statement, because there seem to be some problem with the process once machine is fast. I start externall .exe file from our network drive (slower), and Rebol seems to end before externall utility even starts ... it's strange ... 'call/wait crashes rebol once used inside of button action block ... Anyone? Thanks, -pekr-