Plesk Onyx update on Windows 2008 R2 SP1 64bit

Hi, when I try to update Plesk Onyx 17.8.2 to 17.8 Preview 5 I retrieve the following error:


There are no products for your operating system
( 'Microsoft' 'Windows-server' '6.1-sp1' 'x86_64' ) available
from the selected source.
You can try using another source.


Can you help me?

Thank you!
Stefano