Great aircraft, no doubt. 

I was testing the autopilot system especially the lateral nav using the heading - pre select and bank selector on the right panel, and also the dive-climb pitch. They worked very well until I found that today they were both suddenly inop 10-15 minutes after takeoff. And, the GPS at the same time couldn't be operated, pressing zoom in zoom out didn't change the interface.

All the systems mentioned had been working before, not just once but several times, the issues just occurred today. My guess is this is due to my ignorance. 

many thanks in advance