I had the same symptom on some plants in the Cattleya alliance. The pimples, or "dots," were round, hard, and smaller than a pinhead. They did not rub off or scrub off. In fact, they seemed embedded in the leaf. I was told that it was a form of hard scale. I sprayed the leaves with Enstar II. After a day or so, the dots got brown and sort of dissolved or died, leaving pits in the leaves. My problem might not be the same as yours, but I'll bet it is a pest problem.
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