It sometimes helps to revert to an earlier save where the message isn't there yet. Others have had the same problem with messages popping up (big thread in german forums).
Here's something that 'could' help, can't say if it does (would definately try reloading first in case the workaround may break something).
So, here's what someone found out:
You need : TESV ESS Files Editor (
http://www.nexusmods.com/skyrim/mods/27119/ )
Howto :
1. start program
2. click open
3. choose your savegame with the message on it ( Documents\My Games\Skyrim )
4. open "Global data table 2"
5. open "Interface"
6. click "Data" and look for the "Sirius..." message
7. highlight the message and delete
8. click save and create a new savegame
(translated the instructions as well as I could, I'm no expert, mind^^)
Good luck
