I guess I have good news for you.
I think I solved the problem.
What I have done?
I changed my hosting provider.
I can't imagine why this can be such a problem, but the fact is I copied my Live Site (on 1&1) and I migrate it to another hosting provider of my trust (Dinahosting). And it worked now like a charm.
I'm going to make some more tests to confirm, but I would like to share this information with you before you make any extra work.
That's pretty strange isn't it?
I'm writing THIS message after testing, and seems everything working ok now.
I didn't want to close this ticket just for wait for an answer form you...
It makes any sense all this came from the Hosting Provider?
(I'm not expecting a big and detailed answer form you. With a 'Yes' or 'No' would be enough...)
Thanks a lot for your hard work and dedication, Shane.