I just repainted a vinyl/plastic doll and the paint has remained tacky for two weeks. Any idea why this would happen? I've used your paint for other vinyl dolls with no problem at all.
There may be several reasons for the tackiness. First, the acrylics may not have fully cured. Even after 2 weeks of drying, the acrylic films may not have fully cured if high humidity and low temperature have been present during this time.

Second, the acrylics have a relatively soft, flexible nature about them, especially in warmer temperatures and/or excessive moisture. Unless the acrylics are allowed to have fully cured, such as the use of a heat lamp to warm their drying space for several hours per day for a couple of days, they are more likely to retain a higher level of tackiness.

Finally, certain types of vinyls, when painted with waterborne coatings, may be transferring their "plasticizers" into the acrylics, which can cause the tackiness. We don't have much information on this occurrence, as we have only seen it happen once on a vinyl banner material. In this case, the films lost their tack normally, and only after several weeks did the tackiness develop.

For future applications, you may wish to add some GAC 200 to the paints. This is a specialty acrylic polymer medium that lowers tack and promotes adhesion to the normal paints.