Impersonation Failing In CLR Proc

This is driving me nuts, below is the C# for the proc as well as the runtime error upon calling EXEC on it. Any help would be appreciated. Using UNSAFE Permission Set.

using System;

using System.Data;

using System.Data.SqlClient;

using System.Data.SqlTypes;

using Microsoft.SqlServer.Server;

using System.Security;

using System.Security.Principal;

public partial class StoredProcedures

{

[Microsoft.SqlServer.Server.SqlProcedure()]

public static void uspExternalConnection()

{

WindowsIdentity newIdentity = null;

WindowsImpersonationContext newContext = null;

try

{

//impersonate the caller

newIdentity = SqlContext.WindowsIdentity;

newContext = newIdentity.Impersonate();

if(newContext != null)

{

using (SqlConnection oConn =

new SqlConnection("Server=.\sqlexpress;" +

"Integrated Security=true;"))

{

SqlCommand oCmd =

new SqlCommand("SELECT * FROM AdventureWorks.HumanResources.Employee", oConn);

oConn.Open();

SqlDataReader oRead =

oCmd.ExecuteReader(CommandBehavior.CloseConnection);

SqlContext.Pipe.Send(oRead);

}

}

else

{

throw new Exception("user impersonation has failed");

}

}

catch (Exception ex)

{

SqlContext.Pipe.Send(ex.Message.ToString());

}

finally

{

if (newContext != null)

{

newContext.Undo();

}

}

}

};

Msg 6522, Level 16, State 1, Procedure uspExternalConnection, Line 0

A .NET Framework error occurred during execution of user defined routine or aggregate 'uspExternalConnection':

System.InvalidOperationException: Data access is not allowed in this context. Either the context is a function or method not marked with DataAccessKind.Read or SystemDataAccessKind.Read, is a callback to obtain data from FillRow method of a Table Valued Function, or is a UDT validation method.

System.InvalidOperationException:

at System.Data.SqlServer.Internal.ClrLevelContext.CheckSqlAccessReturnCode(SqlAccessApiReturnCode eRc)

at System.Data.SqlServer.Internal.ClrLevelContext.GetCurrentContext(SmiEventSink sink, Boolean throwIfNotASqlClrThread, Boolean fAllowImpersonation)

at Microsoft.SqlServer.Server.InProcLink.GetCurrentContext(SmiEventSink eventSink)

at Microsoft.SqlServer.Server.SmiContextFactory.GetCurrentContext()

at Microsoft.SqlServer.Server.SqlContext.get_CurrentContext()

at Microsoft.SqlServer.Server.SqlContext.get_Pipe()

at StoredProcedures.uspExternalConnection()