Bill,
Although this problem is not a common problem on the Liberty, it does happen. There can be several different issues that cause this problem from a defective switch, wiring issue (corroded or loose connector), or a shift actuator (motor) defective or stuck. If you are comfortable mechanically with transmission repairs, you can take the actuator off the transfer case and shift the transfer case manually until you can permanently repair the issue. I have seen cases where just removal and replacement of the actuator resolved the issue for an extended period of time. Otherwise, you are off to the Jeep dealer.
Gerald