I'm using my iPhone with a DEH-P5900IB. Same CD-I200 cable.
The iPhone likes to be plugged in before the key is turned on. If I do that, the phone will go to charging and connect to the stereo as soon as I start the car. If I plug the iPhone in after the stereo is getting power, it will sometimes give me ERROR-A0. Easy fix tho, just unplug and replug the iPhone until you get the docking chime and it starts to work.
That being said, it seems some CD-I200 cables don't make a good connection with the iPhone's dock connector. Symptoms of this are bad audio and the stereo getinng stuck at "Ready", the iPod source disappearing, or other errors such as ERROR-11. I had a bad fit with my first phone from almost day one. It was replaced for an unrelated Bluetooth problem, and the new phone worked better... but the cable is worn out and it just started to get bad again today. The problem isn't really the dock connector but the cable: Both phones had a good connection on the CD-I200 cable in my mate's car. So, if you can never get it to connect properly, try another cable.