add error message to exporter, disable export button on launch

Form1.cs

@@ -14,7 +14,7 @@ namespace it_projekt
         private Database db = null;
         public Form1()
         {
-            InitializeComponent();
+            InitializeComponent(); 
             this.exportBtn.Enabled = false;
         }
 
@@ -40,7 +40,7 @@ namespace it_projekt
             if (db.Persons == null)
             {
                 Database.resetDatabase();
-                MessageBox.Show("Connection to Database failed! \nPlease Try again.", "Database Error!");
+                MessageBox.Show("Verbindung mit der Datenbank fehlgeschlagen :( \nVersuchen Sie es erneut.", "Datenbank Fehler!");
             }
             else {
                 foreach (Person person in db.Persons)
@@ -59,6 +59,23 @@ namespace it_projekt
 
         private void export(string Filter, string FileName)
         {
+            List<Person> markedUsers = new List<Person>();
+            foreach (DataGridViewRow row in dataGrid.Rows)
+            {
+                if (row.Cells[6].Value != null)
+                {
+                    if (row.Cells[6].Value.ToString() == "True")
+                    {
+                        markedUsers.Add(db.Persons.Find(person => person.Id == row.Cells[0].Value.ToString()));
+                    }
+                }
+            }
+            if (markedUsers.Count == 0)
+            {
+                MessageBox.Show("Bitte wählen Sie mindestens eine Person zum exportieren aus!", "Exporter Error!");
+                return;
+            }
+
             Stream myStream;
             SaveFileDialog saveFileDialog1 = new SaveFileDialog();
             saveFileDialog1.Filter = Filter;
@@ -69,17 +86,6 @@ namespace it_projekt
             {
                 if ((myStream = saveFileDialog1.OpenFile()) != null)
                 {
-                    List<Person> markedUsers = new List<Person>();
-                    foreach (DataGridViewRow row in dataGrid.Rows)
-                    {
-                        if (row.Cells[6].Value != null)
-                        {
-                            if (row.Cells[6].Value.ToString() == "True")
-                            {
-                                markedUsers.Add(db.Persons.Find(person => person.Id == row.Cells[0].Value.ToString()));
-                            }
-                        }
-                    }
                     StreamWriter sw = new StreamWriter(myStream);
                     if (FileName.Contains("xml"))
                     {