"macOs Sierra failed to download" problem

[picnic]

Guess it's me being stupid again but I spent most of yesterday afternoon trying to upgrade my MacBook Pro to Sierra. The first download failed the security checks so I manually deleted the InstallESD.dmg file. I'm now getting the above error along with

Use the Purchases page to try again

What is this Purchases page they refer to? I assume it's what App Store calls Featured. The option here for Sierra swaps between Install and Download as its mode takes it. Often when I press install I get

macOs Sierra can't be installed to "(null)"

Anyone able help out a hapless Apple user?
TIA

 

[picnic]

Mid 2010 - I'd also hope they'd come up with a better error message if it's not supported than all this garbage.

 

[picnic]

Finally made some progress by visiting a friend who had downloaded the Sierra upgrade and I created a USB Memory Stick upgrade image. This seems to have allowed the MBpro to upgrade. Took an age mind you, at least 4 times longer than the estimates on the screen.