Find the directory with the file acad.vlx. Try to open all AutoCAD files that shows MUST_RECOVER. Type "recover" in the command window on all such AutoCAD files. Hold the CAD window for a bit. Delete ALL the acad.vlx files in your whole computer (also delete it in Recycle Bin so it won't regenerate another file). Then quicksave all the AutoCAD files again. Close all, then try reopening them again and see whether the MUST_RECOVER still appears. If it does, not all the acad.vlx files were deleted.
Find the directory with the file acad.vlx. Try to open all AutoCAD files that shows MUST_RECOVER. Type "recover" in the command window on all such AutoCAD files. Hold the CAD window for a bit. Delete ALL the acad.vlx files in your whole computer (also delete it in Recycle Bin so it won't regenerate another file). Then quicksave all the AutoCAD files again. Close all, then try reopening them again and see whether the MUST_RECOVER still appears. If it does, not all the acad.vlx files were deleted.