Your second para makes it pretty clear why we ask that you post the offending code... or, at least, a snippet that produces the same problem. Your narrative does not cause my crystal ball to show me your script.

Also a problem: you haven't made it clear (or, "clear to me") how para 2 relates to para 1.

It also inspires me to suggest you Super Search with terms like exec and system, as the (implicit) question in para 2 is pretty much a FAQ.