There can be a number of problems. Does this happen for all VIs or just on in particular? If it happens for all VIs, consider reinstalling LabVIEW. If it happens for one VI, it is likely the VI is corrupted and there is usually nothing that can be done for it.
I initally thought that you might have saved the VI without it's block diagram but experiments on my machine show that the File >> VI properties still works.
Inc case you are interested you can save a VI without diagrams by taking a regular VI and going to file >> save with options >> application distribution or just simply selecting "Remove Diagrams".
