Did you happen to save this VI into an LLB for distribution? You could be getting this error because the front panel was stripped (this can happen when you create an EXE or DLL in which the sub-VI's front panel is not needed), or the VI has become corrupt.
You might try running scandisk on your hard drive, I've seen that clean up VI corruption in the past.
Do you know the events that lead up to this error? Did you try to save the VI and get an error? (disk/memory full?) Did the VI work in the past? Is the VI on a network drive? Have you "save with options" or used application builder?
Also, what version of LabVIEW are using?
Thanks!
