I don't remember having this problem before but I haven't animated in MED for awhile. I have a door with a key in it. I want to animate the key turning about 90 degrees. I make my first frame as a keyframe (with the key at 12:00) and then I add 4 more frames (same as the first, but not keyframes0 and then I add my last frame (a keyframe) where I turn the key to the right angle. It should interpolate from the first keyframe to the last, right? But it doessn't. The keys stays right at the 12:00 position until the last frame where it jumps to the new keyframe position. What am I doing wrong?
I take it back. I got it to work exactly once and now it's doing the same thing all over again, even though I am checking "Interpolate vertex positions" WTF??
OK, I'm back on track. The trick is to make your keyframes first (your first and last frames) and then add frames in-between those frames. When you add those in-between frames, that's when you check "Interpolate vertex positions". It turns out that the "key frame" checkbox at the bottom is only for bones animation, so you just ignore it.