.net Mysql Data Reader - Second Query Is To See If There Are Double Bookings In The Database?

I have a basic calendar schedule i want to loop through and then do some checks. My first data reader works fine. But as soon as i put in the second data reader it does not finish.Here is my code

Dim mycommand As New MySqlCommand
Dim mycommand2 As New MySqlCommand
Dim myData As New DataTable[code].....

Basically the above code looks up distinct calendar entries in the database.i then loop through the entries and put the items in a list view.The code above will list about 1600 rows.in the above code if i uncomment the 2 lines the system will break It will on display one line of code. What im trying to do in the second query is to see if there are double bookings in the database.