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Assuming your using releasit and the fiber plus pads from Rick the only thing I can think of would be Host or some carpet sprinkle deodorizer that people use. I would think that some of it would vacuum up though. Also what type of business is it that might give you a clue as to what it is. MAKE SURE THE CARPET HAS DRIED I've heard some products form a film and look better after a while day or two after being applied.
Although I've used releasit on wool and in places that used host and have never had any problems. If you are using some other type of encapsalation product I'm not much help as I stick with what has always worked for me. Let us know what you find out.

The product I used is called ENCAPSOIL-GUARD from POLYMER CONCEPTS. I spoke with the mfg and the white residue is likely sodium from ice melt or rock salt.