Although I just started using Xolox by stumbling on to it, I have seen similar problems in the past with other file sharing programs, Bearshare in particular. It comes from someone (probably your ISP) blocking common file sharing ports. I recommend checking your ISPs use policy as many have banned the use of file sharing applications or severly limit their use. You could also try another file sharing app to see if the same problem exists with it. So far XoloX seems to be more stable than others but without some of the features I like (Kazaa keeps blue screening and Morpheus is a resource hog when sharing a lot of files).