Most likely whatever value you are pulling from the TextBox is not in the table.
Also, I just noticed something. The Select statement should have & signs, not + signs. VB uses "&" to concatenate strings. Changing this should fix the problem. Otherwise, try this. Replace smith in the line below with a username you know is in the table.
Dim MyDatarows() As System.Data.DataRow = BatchAideDataSet.Tables("sa").Select("Username='smith'")
(You can find a username by setting a breakpoint (F9) on this line, highlighting BatchAideDataSet.Tables("sa"), right-clicking and choosing Quick Watch. Then drill down into the table's rows and items until you locate a username - this will be good practice for understanding the object model and examining your code more thoroughly. Or you can take the easy path and look up a username from the database).
You should not have a length of zero after replacing smith in the line above.