Spots on Walnut Table

[Busdriver]

I just finished and delivered a walnut table. I had to go back to the couple's house because they noticed spots on the table.
I used PMK woodworking's 50/50 wipe on poly method. I put about 24 thin coats of oil based polyurethane on, then sprayed the last coat.
The spots look like finger tip marks. I sanded the heck out of this table with 80, 120, 150, 180. Nothing was ever spilled or set on the top during sanding and finishing.
I know it's a long shot but does anyone have any idea what went wrong? I feel sick knowing that this happened to this awesome table.

Thanks
Eddie

[JosephP]

are the spots on the wood or in the finish?

when you said you sanded the heck out of it...are you saying that was before you applied the finish, or this is to fix the spots?

Did you sand at all between coats?

My first guess since you described it as "finger tip marks" is that you had some dust on you fingers and touched the table before spraying.  I would expect wiping would have taken those away which is why I'm guessing it was before the spray.