Why did Colombia's president Santos receive Capriles?

The real reason was to send a clear message to Chavez:

“Listen Hugo.

We know that you are an insufferable asshole and that your campaign methods would send you straight to jail in any semi civilized country. We, your neighbors, and I speak for most of the continent, are not fooled even if we can do nothing about it. However, if in spite of all your treachery Capriles manages to win, we are going to recognize him. Don't you dare steal the election!

I, for one, will not allow you to fuck up what I am trying to negotiate with the FARC. And stealing elections and sending Venezuela into more chaos is not going to help me. So, help me God if you mess up in October 7 at night. If you play dirty be assured that all the files that Uribe left me will be used as necessary. I do not give a rat's ass about who wins, really, but whoever does, he wins.

Got that?”