DateTime.TryParseExact() rejecting valid formats

This is the Simple method, Use ParseExact

CultureInfo provider = CultureInfo.InvariantCulture;
DateTime result;
String dateString = "Sun 08 Jun 2013 8:30 AM -06:00";
String format = "ddd dd MMM yyyy h:mm tt zzz";
result = DateTime.ParseExact(dateString, format, provider);

This should work for you.

Try:

 DateTime.TryParseExact(txtStartDate.Text, formats, 
        System.Globalization.CultureInfo.InvariantCulture,
        System.Globalization.DateTimeStyles.None, out startDate)

Here you can check for couple of things.

1. Date formats you are using correctly. You can provide more than one format for DateTime.TryParseExact. Check the complete list of formats, available here.

2. CultureInfo.InvariantCulture which is more likely add problem. So instead of passing a NULL value or setting it to CultureInfo provider = new CultureInfo("en-US"), you may write it like. .

   if (!DateTime.TryParseExact(txtStartDate.Text, formats, 
                   System.Globalization.CultureInfo.InvariantCulture,
                   System.Globalization.DateTimeStyles.None, out startDate))
   {
       //your condition fail code goes here
       return false;
   }
   else
   {
       //success code
   }