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