Reaper, I suspect ghastley and Kane are correct. The address for your proposed avatar looks okay to me. I would try first changing the size to 90x90.
Then, by way of review, go to upper right corner of your screen in chorrol and pick 'My Controls', look down on left side to Personal Profile and select Edit Avatar Settings. Review the instructions there, plug in your url and hopefully it'll work okay.
Mods are unable to help actually change your avatar. As an Admin, I can delete your avatar but cannot change it. That said, the site is really run by stargleman and I believe he can (and has in the past) worked some magic to change avatars for members. Let's try the other options first and if we still can't make it work, I can ask him to come around and take a look.
Though I'm an Admin here, my putertech is fairly poor so I welcome tips and other ideas like ghastley and Kane have provided.