I've only ever seen "Interrupted system call" on a misconfigured Mandrake system left up for more than a day - after about a day or so, most websites loaded would result in "Interrupted system call" the first time they were loaded. If you figure out what causes it, I'd love to know.
Last I checked exec did not fail gracefully - you'll see the "zombie" behavior if you try to exec a program that doesn't exist, for example (ACS 3.3 did this a lot because the exec command was written improperly so it would try to run "aolserver-errors -15m" rather than "aolserver-errors" with a parameter of "-15m")
