Hello, I'm Jason. I will do my best to answer your question quickly and accurately using the information you have provided.
There are a few possibilities of failure with this code
1) water intrusion into the cabin, which gets into the transmission control module
2) water intrusion into the small oval electrical connector on the left front of the transmission pan area
3) faulty transmission range switch, which is mounted above the left transmission mount, on the side of the transmission case itself
if 1 and 2 are ok, then you'll have to replace the range switch
Can I drive the 320 miles home in this condition, without risk to the transmission, considering my mechanic is at my destination?