I get the "unknown error 805240834 on activation" when trying to activate Outlook.
Scenario as such: I just got a new MBP and migrated my user account from the old machine to the new computer
On the old machine, Outlook would sometimes start in Offline mode, but relaunching the app would fix that.
Also, the "Activate" option was always availabe in the Outlook menu but I never used it as Outlook seemed to work OK.
On the new machine, Outlook is in permanent Offline/Read Only mode and when trying to activate the product, I get the error as above.
Tried downloading from the portal and reinstall, no change in behaviour.
If I try the steps as suggested in
http://community.office365.com/en-us/w/exchange/5867.outlook-for-mac-devices-known-issues.aspx
I get a "xargs: r: No such file or directory" for the first case, and no change in behaviour when I try the second step (which by the way seems not adapted to Yosemite look).