'System.NullReferenceException'

Question

string sqlA = @"UPDATE Meeting SET date = '{1}',

attendees_pax = {2},

start_time = {3},

end_time = {4},

room_id = {5}

WHERE meeting_id = {0}";

int rowsAffected = DBUtl.ExecSQL(sqlA,

TxtMeetingID.Text,

TxtDate.Text,

DrpPax.SelectedValue,

DrpTimeIn.SelectedValue,

DrpTimeOut.SelectedValue,

DrpRoom.SelectedValue);

I cannot get this to update because of  "

An exception of type 'System.NullReferenceException' occurred in System.dll but was not handled in user code

Additional information: Object reference not set to an instance of an object."

Please help me ! i need it asap!