We all pack a picnic, put on our warmest coats, go to get in the Bongo ..... the sliding door is stuck. It just totally will not open.

The knob goes up and down when i lock and unlock but the door just will not budge from the outside or inside.

Subsquently, my relatives have been clambering in through the back door all day which has provided us with literally minutes of amusement but what the hell is going on ?
Anyone else ever experienced this ?