I know the issue you're experiencing, as I reference it in 'Learn how to create a Windows Universal App with IoT & Raspberry Pi ' (https://youtu.be/8mbtOpnYMNU?t=554
Currently, I am unaware of a workaround for this problem (if you don't have the 10240 version of the SDK installed on your dev machine). Therefore, I will ask around and get back to you.
Furthermore, I've also posted a link to your post on the Raspberry Pi forums (
viewtopic.php?f=105&t=132138&sid=7d72f8 ... e87908b69b
) to the Windows IoT slack group.
Lastly Louise, if a copy of my source code from this video (including the web app & azure webjob) would help you with your project let me know and ill get it up on github ASAP!
Want to learn the basics of Windows Universal app development for devices running Windows 10 IoT Core through to how to integrate the solution with Windows Azure? than check out blog.chrisbriggsy.com/Dev-superpowers-Jumping-into-windows-internet-of-things