yum update error in fedora 15

Hi All, I have installed fedora 15x86_64(fresh).And when I tried to update It gives error like this: *[root@localhost ~]# yum update Loaded plugins: langpacks, presto, refresh-packagekit Could not retrieve mirrorlist http://mirrors.rpmfusion.org/mirrorlist?repo=free-fedora-15&arch=x86_64 error was 14: curl#5 - "Couldn't resolve proxy" Could not retrieve mirrorlist http://mirrors.rpmfusion.org/mirrorlist?repo=free-fedora-updates-released... error was 14: curl#5 - "Couldn't resolve proxy" Could not retrieve mirrorlist http://mirrors.rpmfusion.org/mirrorlist?repo=nonfree-fedora-15&arch=x... error was 14: curl#5 - "Couldn't resolve proxy" Could not retrieve mirrorlist http://mirrors.rpmfusion.org/mirrorlist?repo=nonfree-fedora-updates-relea... error was 14: curl#5 - "Couldn't resolve proxy" Error: Cannot retrieve repository metadata (repomd.xml) for repository: fedora. Please verify its path and try again* I am using my net connection behind proxy server. So I also made the changes in yum.conf file for proxy, proxy_username,proxy_password.I did googling for this problem. and i tried solution but they did not work. Could any one please help me to come out from this problem? -- Sandeep Kumar Patel M.C.A. University of Hyderabad Email ID: leosandeep08(a)gmail.com Contact N0.: +91-9491383752