I'm not sure if the thread you linked really describes the same issue. It is true that client certificates use a kind of windows authentication. However I don't know if it is the same problem.

 

Our problems don't really freeze the browsers we tested (IE/FF). Silverligth and Flash just throw errors and the uploader continues the queue until all files have been aborted with an error message.

 

What is interesting is that the errors always appear at the end of the transmission (99%). Since the normal file upload worked we guessed that maybe the server is not able to negotiate the client-certificate with the client for each individual file and thus isn't able to finish the transfer properly.

 

I guess you are not able to reproduce the errors, since you stated that you don't have access to client certificates?