Roger,
You didn't say what wood the plane is chattering on, or what type of grain. Figured woods, or very hard ones often cause chatter. Among the domestic woods, figured maples (birdseye curl, quilting) are among the worst.
Most of what you've been told already is good advice, although I've never felt that waxing the sole reduces chatter. It does make the plane easier to push, though.
1. take very light cuts.
2. if the wood has figure in it, or 'reversed' grain patterning, then try planig from different directions.
3. try wetting the wood slightly - just a light spritz, or a wipe with a wet rag.
4. keep the plane's mouth as tight as possible.
5. keep the chipbreaker about 1/64" (~0.3mm) from the blades edge
6. sharpen often.
7. Since you don't have a high angle frog for your plane, try putting a 3~5° back bevel on the blade. This, in effect, will give you a higher planing angle which iften helps in hard or figured woods.