Getting the OID from a selected feature

I am trying to get the OID of the selected feature to display in textBox2. I am getting an error that says ArcGIS Desktop has encountered a serious application error and is unable to continue. It was strange I got it to work once but I had to continue through an error screen and havent been able to reenact the scenario since. Now it merely crashes everytime. I have made sure a feature is selected as well. I had copied the code in GetSelectedValues() so I am guessing it is how I am initializing the featurelayer. I am new to developing so any suggestions will be greatly appreciated!

public void StartButton_Click(object sender, EventArgs e)
{
IApplication app = (IApplication)this.Hook;
IMxDocument mapDoc = (IMxDocument)app.Document;
IFeatureLayer featureLayer = (IFeatureLayer)mapDoc.SelectedLayer;
GetSelectedValues(featureLayer);
}

private void GetSelectedValues(IFeatureLayer featureLayer)
{
IFeatureSelection featureSelection = featureLayer as IFeatureSelection;
ISelectionSet selectionSet = featureSelection.SelectionSet;

ICursor cursor;
selectionSet.Search(null, false, out cursor);

IRow row = cursor.NextRow();
textBox2.Text = row.OID.ToString();

while (cursor != null)
{
System.Diagnostics.Debug.WriteLine(row.OID.ToString());
row = cursor.NextRow();
}
}