I thought this moment would never come.... but Ambitions is now running properly in my computer
!! It's been 3 days of torture and struggling, but it worked!!!!!!!!! Thank you Pam, I'm really kind of loving you right now. You can't imagine the joy I feel
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Anyway, this is what I did, in case someone finds it helpful. I actually did a lot of things before reinstalling the game, so I don't know what was the decisive thing to do, though.
First of all I made sure my computer had no trace of the Sims, except for the Download Manager. From my experience, DON'T delete the DM or you will experience every human suffering possible. Well, as far as I remember I didn't delete it myself, but it got unistalled somehow and really messed up everything. I made sure the DM was working properly too. Then I did a defrag, scandisk, deleted every temporary file and cooky in my computer and rebooted.
After that, I installed the base game, and updated it as it asked me to. Then I opened the launcher to check how the whole thing was going and realized that some of the CC I had supposedly deleted was still there, so I erased it again just in case. There was not much of it and I doubt that was the real cause of the trouble, but I was not going to take any chances since this was like my 7th attempt at reinstalling. I started the game to check it was running fine.
Then I installed WA. At this point I almost had a panic attack: the WA launcher wasn't working, and I got the same error as before: "there was an error while starting" or something like that, and the launcher closed itself. Luckily enough, my base game launcher was still working, and when I opened it again it asked me to update once more. No idea why it didn't ask me to do this right before the WA install. I installed that second patch and opened the WA launcher, and amazingly it was fixed. So I started the game once more to check everything was fine...
After that I installed Ambitions... and the same thing happened once again. The Ambitions launcher wasn't working, but the base game launcher was, and again it asked me to install a new patch. Once I had done that, the Ambitions launcher was fixed as well, and it now works fine.
Hope this can help you, Simstar. I'm not much of a computer person... I just read a huge amount of topics and posts and managed to be patient. As I said before, I have no idea what exactly made the whole thing work. I just thought it might help others if I posted it here.