I hope someone more versed on the subject then I posts, but here goes until then.
As a Catholic, I do not believe the Pope as a man to be without error or without sin, often referred to as impeccablity. I do believe the Pope speaking ex cathedra to be infallible.
A lengthy but interesting read on the subject can be find at
http://www.newadvent.org/cathen/07790a.htm#I
or
http://www.catholic.com/library/Papal_Infallibility.asp
Who has lead you to believe that the Pope is Infallible or sinless?? Only an IGNORANT person would believe such a thing.
The Pope's Decrees are Infallible...not the Pope. And NO ONE is sinless except for Jesus and the Virgin Mary.
What religion are you, if I might ask?