looks you have connected simple/general error handler .vi to report error messages
Remove this from ur VI and this pop up will not appear
If you are using easy file i/o VI's( found in the first row of file I/O functions palette) like read/write to spread sheet file, they will have this error handler VI's inbuilt.
If this is the case, build a simple file read Vi using intermediate File i/O vi's. Here, do not include the error handler VI's