His reps say, quote, "We are not sure what's wrong with him at this stage and are worried.  We don't know if it is a recurrence of the previous problem or if it is something else entirely."

Robin has had stomach problems before.  Last year, he underwent emergency surgery for a blocked intestine.  He had to have part of his intestine removed.

Robin's twin brother Maurice Gibb had an intestinal problem back in 2003 and he DIED from it.

Robin was supposed to leave for Brazil on Sunday, but he canceled the tour on his doctors' advice.