Urethane comes in both flavors. There are many factors that can affect the dry/cure time of finishes. Temperature, humidity, age of the product. Also, rattle cans have extra solvents in them, so they atomize(spray). Depending on what the old finish was and how throughly it was removed can have a big effect also. All those solvents will soften the remaning old finish, which can get trapped under the new finish. Not letting one coat dry before applying more coats, can have the same trapping effect. Give it some time and if it does not cure out, do what Pat B. said. Shellac is a universal sealer/bridge coat, but make sure it is dewaxed, or you will be very sad.