Based on what you've shown us, I'm of two minds:
- There appears to be a space (or some other char which didn't get rendered here) in the location before the head of the second arrow -- the one actually pointing out whatever it is that the regex engine thinks is "unmatched" in which case, diagnosing the problem will likely require a verbatim rendition of the error message (wrap error messages in code tags for our ease of reading).
- Alternately, the message says your regex is missing a parenthesis: I can't see that as accurate yet, because you show us an open paren as the second "word" in the error message, and another open at the second arrow, closed after the second "VISITADOS" ...
If I've misconstrued your question or the logic needed to answer it, I offer my apologies to all those electrons which were inconvenienced by the creation of this post.