I'm having the same issue as you, and I've had it before. The first time I got the Sims 3 I was running Vista, and when I tried to play the vanilla game I got the error message:
"The sims 3 launcher has encountered a problem and needs to close." It then went on to ask me to file an error report, etc, etc. It was a while back, but if I remember correctly the solution was to right-click the icon of the game launcher and select 'run as administrator- (even though I was on an administrator account, damn Vista!). I don't think that alone was enough though, because I had to go to compatibilities and check... Windows 2000 mode, I think it was.
I hope that helps you, if you have Vista that is. I'm now running Windows XP and am having exactly the same problem, and I have no idea how to fix it. 

I recently gathered my courage and turned my attention back to the Sims. I deleted all my mods, went to simprograms and installed the 2.3 - 2.4 mod (region .002). That went fine, and since I'm running Vista Home Premium, EADM decided to work again.  So I downloaded the two patches available, the CAW one and the update to 2.6.11.005002.
And now my game won't work at all. I'd abandoned it in the first place because of the 'blue lot syndrome', and the fact that I had no internet at the time and couldn't fix it. But now, whenever I try to boot it up, an error message says,
"Your The Sims 3 Base Game is incompatible with the current Sims 3 Expansion Pack. Please update your game via the game launcher."
Of course, there are no more updates in the launcher. When I first got the WA expansion - which is the only one I have - I had to hack into the SKU in regedit to allow it to play. I've checked, and the SKUs on both the base and expansion are 2.
Help? This is driving me mad!

The same thing happened to me - AFTER I'd sorted out the getting-the-region-code-to-work business. EA is really pissing me off lately. :/
What I did was go to Simprograms (www.simprograms.com) and went to patches. I downloaded both the .001 and .002 version of the patch, because I wasn't sure which one worked. I found the right one and now my game works fine. Until the next fiasco.

I just wanted to say thanks to the people who replied to this thread. I've searched in a lot of places for the answer to this irritating issue and this is the only place I've found it. THANK YOU!
EA has some serious issues it has to deal with.