Right, i can do technical, just not talk it so bear with me lol.
I used to have a Vectra V6 cdx auto with exactly the same problem. Start car, put into D, autobox fault shows on mid and car goes into limp mode. However, if i left the car to warm up for about 10 minutes, could put into drive and no problem whatsoever.
After a bit of research, it pointed to the auto selector. The lube inside had lost its lube qualities and only regained them when it had warmed up before engaging Drive. Vauxhall say it is a non servicable part however, if you have a steady hand and patience, you can seperate (watching out that you dont lose or misplace the brass contacts and springs that sell the car when it can be turned on for example) you can clean it out and replace with a better quality grease)
Hope this helps somewhat