Received a new N810 out of the box, upgraded it online to 30.2 successfully, then tried the next step to 36.5 and got:"Feature upgrade not possible, missing program packets, pre-installed-documentation-rx44 (=5.4)".
Looked in old threads but could not find solution.
Any hints?
Thanks in advance.

You'll be wanting version 43.7, 36.5 is old now. As your N810 is new, I'd recommend reflashing it with the new software to avoid any conflicts with upgrading (as you're already experiencing).

For more information look here.