Update to Fedora 19 failed with curl 403 error

Update to Fedora 19 failed with curl 403 error

I tried to to update my Fedora 18 to 19 using fedup but I am getting an
error from curel "The requested URL returned error: 403 Forbidden"
I am behind a firewall and http_proxy enviornment variable. It works in
other application.
root@localhost ~]# fedup-cli --network 19 setting up repos... No upgrade
available for the following repos: sublime2 getting boot images...
.treeinfo | 1.1 kB 00:00
Downloading failed: couldn't get boot images: curl#22 - "The requested URL
returned error: 403 Forbidden"