Probably your firewall settings (perhaps ad blocking or similar).

You might try placing WinCustomize in your "trusted sites" list.

If you need the IP addresses, I believe these are still correct:

www.wincustomize.com 66.28.242.218
images.stardockcentral.net 66.54.81.54
images.stardock.com 66.54.81.60
skins3.wincustomize.com 66.28.242.211

For the ObjectDock themes - use the "Advanced Search Options" link in the search box at top of library, which will expand the section and offer check boxes for various categories - including "themes".