I just ran into a problem with the plugin for eWay (2.65). The store name setting contained an ampersand which causes the gateway to respond with an error:

Payment error: An invalid response was recieved from the payment gateway.Error: XML not formated correctly to eWAY standards. Reason:Whitespace is not allowed at this location. Error Code:-1072896749(Test CVN Gateway)

To fix I have altered \Plugins\Nop.Plugin.Payments.eWay\GatewayConnector.cs Line 50
byte[] requestBytes = Encoding.ASCII.GetBytes(Request.ToXml());

byte[] requestBytes = Encoding.ASCII.GetBytes(Request.ToXml().Replace("&","and"))

This should prevent errors from occurring if any part of the order contains an ampersand (eg: address, name etc)