I have been using the double shot and double walled basket because it is more forgiving. I have used the single shot - single wall basket with the beans I got locally roasted and was able to get 9 bar when I first got the machine. Mostly I stuck with the double wall basket because it worked better for the non-local beans i have. For a month and a half I've been able to consistently get 7 bar every time with the double walled double basket.
-I read the manual cover to cover
-I have been backflushing the machine regularly
-I ran a cleaning tablet through just to be sure.
Here is a video with the backflush disc inserted. http://www.youtube.com/watch?v=evyjU22sAQ8
I'll pick up a new grinder and experiment with it. Hopefully that fixes my issue though I'm not sure why the pressure during the backflush can't make 10 bars anymore.