Added musings on runnig as Console app.

NTwain/AsyncPump.cs

@@ -0,0 +1,50 @@
+//using System;
+//using System.Collections.Generic;
+//using System.Linq;
+//using System.Text;
+//using System.Threading;
+//using System.Windows.Threading;
+
+//namespace NTwain
+//{
+//    // from http://blogs.msdn.com/b/pfxteam/archive/2012/01/20/10259049.aspx
+
+//    /// <summary>
+//    /// Provides a pump that supports running asynchronous methods on the current thread.
+//    /// </summary>
+//    public static class AsyncPump
+//    {
+//        /// <summary>
+//        /// Runs the specified asynchronous function.
+//        /// </summary>
+//        /// <param name="func">The asynchronous function to execute.</param>
+//        /// <exception cref="System.ArgumentNullException">func</exception>
+//        /// <exception cref="System.InvalidOperationException">No task provided.</exception>
+//        public static void Run(Func<Task> func)
+//        {
+//            if (func == null) throw new ArgumentNullException("func");
+
+//            var prevCtx = SynchronizationContext.Current;
+//            try
+//            {
+//                var syncCtx = new DispatcherSynchronizationContext();
+//                SynchronizationContext.SetSynchronizationContext(syncCtx);
+
+//                var t = func();
+//                if (t == null) throw new InvalidOperationException();
+
+//                var frame = new DispatcherFrame();
+//                t.ContinueWith(_ => { frame.Continue = false; },
+//                    TaskScheduler.Default);
+//                Dispatcher.PushFrame(frame);
+
+//                t.GetAwaiter().GetResult();
+//            }
+//            finally
+//            {
+//                SynchronizationContext.SetSynchronizationContext(prevCtx);
+//            }
+
+//        }
+//    }
+//}

NTwain/NTwain.csproj

@@ -53,6 +53,7 @@
     <Reference Include="WindowsBase" />
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="AsyncPump.cs" />
     <Compile Include="Data\TypesExtended.cs" />
     <Compile Include="DeviceEventArgs.cs" />
     <Compile Include="Extensions.cs" />

NTwain/TwainSession.cs

@@ -309,10 +309,7 @@ namespace NTwain
         /// <exception cref="ArgumentNullException">context</exception>
         public ReturnCode EnableSource(SourceEnableMode mode, bool modal, HandleRef windowHandle, SynchronizationContext context)
         {
-            if (Environment.OSVersion.Platform == PlatformID.Win32NT)
-            {
-                if (context == null) { throw new ArgumentNullException("context"); }
-            }
+            if (context == null) { throw new ArgumentNullException("context"); }
 
             Debug.WriteLine(string.Format("Thread {0}: EnableSource.", Thread.CurrentThread.ManagedThreadId));
 
@@ -378,6 +375,8 @@ namespace NTwain
         /// <summary>
         /// Forces the stepping down of an opened source when things gets out of control.
         /// Used when session state and source state become out of sync.
+        /// This should be called on the Thread that originally called the <see cref="EnableSource"/>
+        /// method, if applicable.
         /// </summary>
         /// <param name="targetState">State of the target.</param>
         public void ForceStepDown(int targetState)