You can't log in to ColdFusion 8 or 9. You are using the correct RDS (Remote Development Services) password.
This issue is rare, but is the result of the way ColdFusion serializes an object to wddx. The problem happens when the CFC (ColdFusion Component) is accessed as a webservice before its metadata is requested from the Flex side. When the CFC is accessed as a webservice, webservice-related metadata (which can't be serialized) is added.
For more information, see bug FB-23626.