We are using a 7855 upgraded to firmware 072.040.004.09100. We do not use a network proxy.
Which device are you using? It sounds to me like it's not configured correctly. Have you been able to scan to dropbox in the past? I would check the proxy settings on the device if you have a network proxy. Check under the Extensible Services setup and in Connectivity>HTTP Proxy to make sure it's set in both places.
We are trying Scan to Dropbox. I can log in thru the connectkey app and see my dropbox folders. When I pick one and hit start I get the following error on the printed error notice. Unable to connect to remote server The server name is xas-mid-prod.services.xerox.com:443 .....HELP......