I have a problem with some wiring that I ran for an outside motion light. Although the hot leg and ground wires are fine, the neutral wire is defective ( it may have gotten knicked or something). Of course, now the wiring is covered up behind a wall that I do not want to tear into if it can be avoided. Can I use the ground wire as the neutral wire? If not does anyone have any suggestions besides tearing a wall down? Thanks much!

I would check neutral carefully, usually the connections are the source for problems, wires usually doesn't break in the middle.
Check all neutrals real good in both boxes.

Just to confirm. NO, you can absolutely 100% NOT use a bare ground as a neutral in ANY shape or form.

Find the problem and fix it.
From an experienced standpoint, it is very unlikely that you will have to open walls and tear out sheetrock to find it. Unless of course someone illegally buried a box.