I just gave it a try and for whatever reason it wouldn't work.
I changed the avatar to a 'stock' avatar with success. From there I was able to reload my mug.
You may want to kill any apps that would be uploading data which could interfere, especially if it runs on the same port, or even give another browser a whirl. Of course there is always the ever popular restart.
Let me know if this is/isn't of any help.