Every once in awhile, VIs get corrupted (usually due to a disk I/O error). In LabVIEW-speak, you probably have an insanity, something that “cannot be”, but is. Many times, you can cure the problem by creating a blank VI, selecting everything in the insane VI, copying it, then pasting to the blank VI. This process causes LabVIEW to do a sanity check of everything and will sometimes fix it. If this doesn't work, you will probably need to rewrite the VI.