From what you say, there shouldn't be any memory leak issues, and the rate at which you're collecting data shouldn't be causing any trouble. Likewise the amount of data you're plotting is really rather modest.
Ok, Step 1: Write a replacement subVI that is a drop in replacement for the DAQ subVI and generates the 6 values at the exact same rate, but uses a random number generator to produce the datavalues. Insert this dummy into your code instead of the DAQ and let it run. This will isolate one large part of the code and a good approach in troubleshooting something like this is always "divide and conqure".
If this version works without crashing, you know its in the DAQ somewhere. If it still crashes, you have something that other people c
an look at and try to verify there isn't something hinky going on with your PC (Step 2).
Mike...