Tom,
There is not much the system would be able to do since you are limiting the pipe sizes, and then sizing that zone with a flow that exceeds what will work through those available sizes. When you say NO to that message, you can press F2 to pull up the command list, where it will show you what valve it stopped on.
From there you should be able to make the design decision on making smaller zones or including bigger pipe sizes in your available pipe size list from Pipe Data.
If we are missing something, feel free to send in the plan and we are happy to discuss further.