After spending a solid 6 hours trying to solve this I finally got it!
The trick is to use Sunray Flashup for DM800 SE instead of DreamUp.
It can be found here:
SUNRAY-FlashUP.rar - 4shared.com - online file sharing and storage - download
(Sorry if Im not supposed to post links like that.)
As the DM 800HD SE is relatively new and will most likely be very popular in the future it might be worth while for the mods to write up a sticky explaining how to solve CA NOT FOUND on DM800 HD SE.
Hope this helps anyone who finds themselves down the same road.