When working with the Dataview web part I got the error below
This page allows a limit of 200 controls....
I experienced this when adding a lot of "Related Data Sources". I tried adding the dataview web part created using multiple document libraries on a number of pages but got the same error.
But once I started from scratch again and created the first data source and added the "Related Data Sources" one by one again, it seemed to work, no idea why!