Hello,
This problem has been found to occur if you open a VI with globals in 7.0 that was written in LV 5.1 or 6.0. Unfortunately, the only workaround is as Dennis describes, which is to copy the block diagram entirely into a new VI in version 7.0.
Our R&D team has been working on this issue and it will be fixed for a future version of LabVIEW.
I hope this helps! Please let me know if there is anything further I can do for you.
Liz F.
National Instruments