If you were previously using hyper-terminal then your messages are probably line feed terminated.
Make sure that the serial init is set to use a terminator and the term char is 0xA. Don't bother with the bytes at serial port property node and wire a huge number (say 1024) to the bytes to read of the Visa read.vi. The number has to be big enough to receive your longest message and don't worry......the read will automagically return on the term char if its less.
There is a serial example in Labview. "National Instruments\LabVIEW 8.2\examples\instr\smplserl.llb". Notice they don't use the bytes at serial port!