by Shashikant Vaishnav.
Hi jim,
I just made a try to put your logo in Formal White theme with the link 
and its work fine.
If you will look over the source. The theme directly hits the link to find the image[rather then storing it in any directory or cache]. I am sure you are making mistake with source of the logo. please double check the source to your logo.
good luck
Shashikant