I took a look at your application and couldn't really tell what was outputting to your current (A) string (the subVIs were missing). The best thing I could suggest is setting breakpoints and probes to see if the values you are expecting are coming out of the subVI that is outputting to your indicator. Another thing to keep in mind is that the chart won't update on the front panel until the subVI finishes executing. If there is a loop in your subVI, it is expected that the indicator will not update until the subVI finishes executing.
As for the error 7 that you are receiving, what is the file path? Generally that error occurs when there is an invalid file path, but it looks like you are using a file dialog prompt to select a file path. Does it occur the first time your program iterates through your loop or after that? Another thing I noticed is that you open and close the reference to the file inside of the while loop. Generally this is not good programming practice as we would recommend only opening and closing each file once and place the Open and Close VIs outside of the while loop.
Stephanie A.
Americas Marketing Manager
National Instruments
