It seems that InstallShield has, for some time, had a habit of sometimes returning this spurious exit code on (apparent) success (at least since v. 9:
http://www.kinook.com/Forum/showthread.php?threadid=438). kevina's post shows how to work around this specific exit code in VBP rather than marking the step to ignore all failures (you may also want to check LASTSTEP_OUTPUT for success/failure indicators).
You might try updating to the latest version (not sure which version you have) of IS or open a support incident with the InstallShield folks in the hope that they will finally fix the problem. BTW, -1073741819 decimal equals C00000005 hex (most likely an access violation).