First of all, when your while loop stops, the False condition will not be executed automatically. Also, you don't have anything wired to the condition terminal of the Case structure. If you want to execute the code in the True case, then when the stop button is pressed execute the False case, I would advise that you get rid of the case structure entirely. Use a flat sequence structure and put the code from the True case in the first sequence. Put the code from the False case in the second sequence. Or better yet, instead of using flat sequences, use data flow. Put an Error In and Error Out terminal in your subvi and main. Wire Error In through the loop. Wire error output from loop to error in of the subiv, wire error out of subvi to error in of DAQ express vi.
Another point is do you really need to execute the relay close code inside your loop? If not, put it before the loop so that it doesn't continuously send commands to close relays that are already closed. Use error ins and outs to create data dependant execution flow.
