You need to actually sign in to the site.
I had the same problem. Wincustomize said because I hadn't bought anything, I've reached my "download limit" for free stuff, and that if want to continue free downloads I need to make a donation for all the people who keep the site going, someting like $7.50 a month to continue, because I'm not a customer. (lol - donation)
But I did buy something, Deskscapes!! So, I thought about it for a while and then noticed the "log in" button. After logging in, the button would say "log out", right? So I logged in and the site recognized me as a customer/member with unlimited downloads. I haven't had a problem since.