I created a webviewer with a length of 400 pixels, and below it is a relatively large canvas.
You probably have screen1 set as scrollable. Uncheck this, then the webviewer will scroll.
Thanks. I have solved the problem through your method, even if scrolling is canceled, the canvas below cannot be used in screen 1. 
You can try this:
Set Screen1 to Scrollable and Screen1 centred. Set the webviewer and canvas to @ 90% width, to provide something to scroll on left and right.You must set the webviewer height to automatic in the designer, then when the page first renders, it returns the full height of the web page, and sets the webviewer to that height. You can then scroll the web page until you reach the canvas, then continue scrolling the canvas. You might set the canvas as not visible to start with, otherwise it displays while the webviewer is resized.
Unfortunately, you have picked the two components that do not like to be scrolled!
WoW! Thanks for your code. I'll try it later! 
