Don't kill non-existing timers. Use EndDialog to close the dialog.

diff --git a/programs/taskmgr/taskmgr.c b/programs/taskmgr/taskmgr.c
index a478d15..66674ec 100644
--- a/programs/taskmgr/taskmgr.c
+++ b/programs/taskmgr/taskmgr.c
@@ -244,7 +244,7 @@
             OnAbout();
             break;
         case ID_FILE_EXIT:
-            DestroyWindow(hDlg);
+            EndDialog(hDlg, IDOK);
             break;
         }     
         break;
@@ -564,23 +564,12 @@
     TabCtrl_SetCurFocus/*Sel*/(hTabWnd, 2);
     TabCtrl_SetCurFocus/*Sel*/(hTabWnd, nActivePage);
 
-    if (TaskManagerSettings.UpdateSpeed == 0)
-        KillTimer(hWnd, 1);
-    else if (TaskManagerSettings.UpdateSpeed == 1)
-    {
-        KillTimer(hWnd, 1);
+    if (TaskManagerSettings.UpdateSpeed == 1)
         SetTimer(hWnd, 1, 1000, NULL);
-    }
     else if (TaskManagerSettings.UpdateSpeed == 2)
-    {
-        KillTimer(hWnd, 1);
         SetTimer(hWnd, 1, 2000, NULL);
-    }
     else if (TaskManagerSettings.UpdateSpeed == 4)
-    {
-        KillTimer(hWnd, 1);
         SetTimer(hWnd, 1, 4000, NULL);
-    }
 
     /*
      * Refresh the performance data