I too also did this, and my issue still persists as well. Are there more installation actions besides the two .exe files that i need to give admin permission to?
Well i also had to do the 'reinstall' of all the DLC's from the in-game store also. That and have the 1.10 patch.
The first time i installed it was on my Internet profile on my laptop (this is not an Administrator user Profile) while i was seeing about copy/pasting the entire install to my non-internet PC. I couldn't get all the DLC, in particular The Old Gods one, to work in game, even when they would show up in the launcher screen (ticks in boxes).
The second time i installed i was in my Administrator Profile on my laptop and by installing and making sure all the .exe files (CK2.exe and CK2game.exe)were running with Administrator privileges (right click on lauch icon>properties>advanced>tick box 'run as administrator' - along those lines), then going into the in-game store to 'reinstall' all the green and ticked DLC, then relaunching the game and adding the 1.10 patch, on the next relaunch of the game i suddenly had all the DLC working in game (my four icons to the bottom left of the screen on entering a single player game, and when i mouse over muslim or pagan provinces i don't get the red warning text).
This means i have to enter my admin password if launching the game in the non admin profile etc.
Also it might be a good idea to do all this from a completely clean reinstall, just in case any of the left over stuff from a previous attempt messes it up? I've got it all working on two pc's now (i just wanted it on the one gaming PC and will delete if of the laptop as it is not powerful enough to play it), one under Vista and one under XP.
This is the GG version, with all GG DLC. Steam may be more complicated? But it was the Admin stuff that really made the difference for me. I have no idea why i have to 'reinstall' all the DLC from the in-game store, but they would not appear in the in-game launcher screen (CK2game.exe) unless i did that first.
I'm just hoping to avoid the crashing issues i've been reading about with the 1.10 patch! I really do not want to lug my gaming rig downstairs again to connect to the net!