Hello Gstan, Thank you for contacting National Instruments.
I was able to open your VI in LabVIEW 5.1. It behaves as you described. Try holding down the shift key and right-clicking on the block diagram. This will bring up the tools palette. Select the arrow and you should now be able to select items. I would try to copy and paste various parts of your block diagram into a new VI. Go piece by piece. See if you can modify it in a new VI. I hope this helps, Sean C. Applications Engineer National Instruments
