[Windows Phone 7 Software Development] scilor:
Thank you for this hint, I am already using it on my Windows Mobile apps in an older version. (Everything worked with that old version very fine, the api now is the same on wp7)

There is now a different error:

Newtonsoft.Json.JsonSerializationException was unhandled
Message=Error getting value from 'parameters' on 'SciLorsGroovesharkAPI.Groove.GroovesharkRequestBuilder`2+ConnectGroovesharkRequest[SciLorsGroovesharkAPI.Groove.Functions.CommunicationToken+GetCommunicationTokenParams,SciLorsGroovesharkAPI.Groove.Functions.CommunicationToken+GetCommunicationTokenResponse]'.
StackTrace:
at Newtonsoft.Json.Serialization.ReflectionValueProvider.GetValue(Object target)
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContract collectionValueContract)
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContract collectionValueContract)
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize(JsonWriter jsonWriter, Object value)
at Newtonsoft.Json.JsonSerializer.SerializeInternal(JsonWriter jsonWriter, Object value)
at Newtonsoft.Json.JsonSerializer.Serialize(JsonWriter jsonWriter, Object value)
at Newtonsoft.Json.JsonSerializer.Serialize(TextWriter textWriter, Object value)
at SciLorsGroovesharkAPI.Groove.GroovesharkRequestBuilder`2.WriteRequestContent(Object SendObject)
at SciLorsGroovesharkAPI.Groove.GroovesharkRequestBuilder`2.MakeRequest()
at SciLorsGroovesharkAPI.Groove.GroovesharkClient.GetCommunicationToken()
at SciLorsGroovesharkAPI.Groove.GroovesharkClient.Connect()
at SciLorsGroovesharkAPI.Groove.GroovesharkClient.CheckConnect()
at SciLorsGroovesharkAPI.Groove.GroovesharkClient.SearchArtist(String Search, Int32 Limit)
at SciLor_s_GrooveMobile_WP7_C.MainPage.<btnSearch_Click>b__0()
InnerException: System.FieldAccessException
Message=SciLorsGroovesharkAPI.Groove.GroovesharkRequestBuilder`2+ConnectGroovesharkRequest.parameters
StackTrace:
at System.Reflection.RuntimeFieldInfo.GetValue(Object obj)
at Newtonsoft.Json.Utilities.ReflectionUtils.GetMemberValue(MemberInfo member, Object target)
at Newtonsoft.Json.Serialization.ReflectionValueProvider.GetValue(Object target)
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContract collectionValueContract)
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContract collectionValueContract)
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize(JsonWriter jsonWriter, Object value)
at Newtonsoft.Json.JsonSerializer.SerializeInternal(JsonWriter jsonWriter, Object value)
at Newtonsoft.Json.JsonSerializer.Serialize(JsonWriter jsonWriter, Object value)
at Newtonsoft.Json.JsonSerializer.Serialize(TextWriter textWriter, Object value)
at SciLorsGroovesharkAPI.Groove.GroovesharkRequestBuilder`2.WriteRequestContent(Object SendObject)
at SciLorsGroovesharkAPI.Groove.GroovesharkRequestBuilder`2.MakeRequest()
at SciLorsGroovesharkAPI.Groove.GroovesharkClient.GetCommunicationToken()
at SciLorsGroovesharkAPI.Groove.GroovesharkClient.Connect()
at SciLorsGroovesharkAPI.Groove.GroovesharkClient.CheckConnect()
at SciLorsGroovesharkAPI.Groove.GroovesharkClient.SearchArtist(String Search, Int32 Limit)
at SciLor_s_GrooveMobile_WP7_C.MainPage.<btnSearch_Click>b__0()
InnerException: