Here is my code

public void KeyPress()
    {
        //Finds the target window and sends a key command to the application
        Process[] processes = Process.GetProcessesByName("calc");
        IntPtr calculatorHandle;
        foreach (Process proc in processes)
        {
            calculatorHandle = proc.MainWindowHandle;

            if (calculatorHandle == IntPtr.Zero)
            {
                MessageBox.Show("Calculator is not running.");
                return;
            }
            SetForegroundWindow(calculatorHandle);

            break;
        }

        SendKeys.SendWait("1");

    }

After Executing this code I recieve an Error, i know the source is the SendKeys.

Here is the full error I am Receiving

System.InvalidOperationException was unhandled
  Message="The Undo operation encountered a context that is different from what was applied in the corresponding Set operation. The possible cause is that a context was Set on the thread and not reverted(undone)."
  Source="mscorlib"
  StackTrace:
       at System.Threading.SynchronizationContextSwitcher.Undo()
       at System.Threading.ExecutionContextSwitcher.Undo()
       at System.Threading.ExecutionContext.runFinallyCode(Object userData, Boolean exceptionThrown)
       at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteBackoutCodeHelper(Object backoutCode, Object userData, Boolean exceptionThrown)
       at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Net.ContextAwareResult.Complete(IntPtr userToken)
       at System.Net.LazyAsyncResult.ProtectedInvokeCallback(Object result, IntPtr userToken)
       at System.Net.Sockets.BaseOverlappedAsyncResult.CompletionPortCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* nativeOverlapped)
       at System.Threading._IOCompletionCallback.PerformIOCompletionCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* pOVERLAP)
  InnerException: 

I'm not sure what the problem is, The number will appear in my calculator but that error pops up