We're having the exact same problem here, except one twist:

 

We use identity impersonate on our intranet.  I, as the intranet webmaster have admin rights on our server that hosts the intranet.  From my pc, I can upload files when Identity impersonate is true, and I think it's because I have an admin account on the server.

 

All other users of our intranet that use the CE have this error.

 

Other than that I wanted to say that the editor is fantastic.  We're very satisfied customers, but we're also anxiously awaiting this bug fix as this was a key selling point for us.

 

Thanks, and keep up the great work!

 

Adam