I had a similar problem, starting a sub-vi parallel to the system exec.vi, esp. communicate with a power supply to switch on after my firmware loader (external apllication) waits for the power-up sequence of the D.U.T. The problem was to wait for the completition of the loader for getting any error information over the standard error output ("successfully programmed" e.g), and turn on the power supply few msec after loader starts ....... thx for your hint
best rgds Peter