If you're getting the following error, it probably means that you have a RemoteObject call within your flex application that's loaded up as a workspace task (process / form / etc). You won't see this error if you're using the same credentials to log into workspace as what you're using for your remoting call, but it'll pop up if you try to log into workspace with another random user.
That being said, you should not authenticate your endpoints in flex and simply ensure that all users who need access to your workspace task have both "Services User" and "LiveCycle Workspace User" roles assigned to them.
fault = (mx.rpc::Fault)#2
errorID = 0
faultCode = "Channel.Authentication.Error"
faultDetail = "Cannot re-authenticate in the same session."
faultString = "warn"
message = "faultCode:Channel.Authentication.Error faultString:'warn' faultDetail:'Cannot re-authenticate in the same session.'"
name = "Error"
rootCause = (mx.messaging.messages::ErrorMessage)#3