ReportingService.ReportingService rs = new ReportingService.ReportingService();

Item has already been added. Key in dictionary: ":" Key being added: ":"
Stack Trace: 
[ArgumentException: Item has already been added.  Key in dictionary: ":"  Key being added: ":"]
   System.Collections.Hashtable.Insert(Object key, Object nvalue, Boolean add) + 955 
   System.Collections.Hashtable.Add(Object key, Object value) + 11 
   System.Collections.DictionaryBase.System.Collections.IDictionary.Add(Object key, Object value) + 111 
   System.Xml.Serialization.TempAssembly.InitAssemblyMethods(XmlMapping[] xmlMappings) + 186 
   System.Xml.Serialization.TempAssembly..ctor(XmlMapping[] xmlMappings, Type[] types, String defaultNamespace, String location, Evidence evidence) + 155 
   System.Xml.Serialization.XmlSerializer.FromMappings(XmlMapping[] mappings, Type type) + 193 
   System.Xml.Serialization.XmlSerializer.FromMappings(XmlMapping[] mappings) + 22 
   System.Web.Services.Protocols.SoapClientType..ctor(Type type) + 968 
   System.Web.Services.Protocols.SoapHttpClientProtocol..ctor() + 151 
   BCS.WebApp.ReportingService.ReportingService..ctor() in c:\projects\bcs.ddc\bcs.webapp\web references\reportingservice\reference.cs: 42 
   BCS.WebApp.Reports.ReportBase.OnLoad(EventArgs e) in c:\projects\bcs.ddc\bcs.webapp\reports\reportbase.cs: 63 
   System.Web.UI.Control.LoadRecursive() + 35 
   System.Web.UI.Page.ProcessRequestMain() + 750