I have owned my car for a couple of years now. Why have I only just realised you can get the roof up/down whilst moving, albeit very slowly, very useful.
I had the same experience and there is a post from me on this forum with a chaps name and number who fixed it for me. I tried to do it myself initially but made matters worse.
After about 18 months I now occasionally get a error 4 message again but fortunately it clears itself after a while.