Hi, Fran. A couple of questions. Did you sand the previous finish or did you sand down through it into the wood? Did you use oil or water based poly?
My suspicion is that the mineral spirits was not completely dry when you applied water based poly. You can do this with oil based but not water based. Tack cloths are much better at picking up dust after you vacuum. You can use mineral spirits if you are going to apply an oil based finish.