Yes there is a log file that would have low-level details about any transfer failures. One way to look at it is to run "Help->Collect log files..." from the menu and then look in the zip file for the Stash.log file.
Sometimes there can be a temporary issues with an upload that resolves itself automatically after a period of retries. I'm not sure from your description whether it could be because of a network connection issue, the servers themselves or a sharing violation on your machine. If the situation persists then we can help looking at the logs to see what is happening.
-Andrew
Mozy R+D