Vb.net and mysql issue

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VB

MySQL

I wrote the following to test/workout a problem I've been having dealing with a MySQL database.

I can update a single record without a problem but when I try to update multiple records I get a Concurrency violation

The only field I'm trying to update is a date field which was left null, I created the same 'setup' with the test database table (null dates) and it ran just fine.

The original table is more complex than the test database (multiple indexes and more fields) but I set the permissions exactly the same, using the same user account/password...

Here's the 'test' code - it was written on a windows form but I stripped all the b.s. out of it... UpdateMySQL was called with either a 1 or 2, 1 worked, 2 failed.

Imports MySql.Data.MySqlClient
Public Class mysql_test
    Public Sub UpdateMySQL(TestPass)
        Dim myTableName As String
        If TestPass = 1 Then
            myTableName = "test_table"
        Else
            myTableName = "live_table"
        End If
        Dim SQL As String = "Select * from " & myTableName
        Dim Conn As MySqlConnection
        Dim myDataAdapter As New MySqlDataAdapter
        Dim MySQL_Command As New MySqlCommand
        Dim MyDataTable As New DataTable
        Conn = New MySqlConnection()
        If TestPass = 1 Then
            Conn.ConnectionString = "server=mysqlserver;user id=userid;password=useridpassword;database=testdb;"
        Else
            Conn.ConnectionString = "server=mysqlserver;user id=userid;password=useridpassword;database=livedb;"
        End If
        Try
            Conn.Open()
            MySQL_Command.Connection = Conn
            MySQL_Command.CommandText = SQL
            myDataAdapter.SelectCommand = MySQL_Command
            myDataAdapter.Fill(MyDataTable)
            With MyDataTable
                Dim r As Integer = .Rows.Count
                For x = 0 To .Rows.Count - 1
                    If TestPass = 1 Then
                        .Rows(x).Item("date2") = .Rows(x).Item("date1")
                        .Rows(x).Item("date1") = Now
                    Else
                        .Rows(x).Item("date_modified") = .Rows(x).Item("date_entered")
                    End If
                Next
            End With
            Dim cb As MySqlCommandBuilder = New MySqlCommandBuilder(myDataAdapter)
            myDataAdapter.Update(MyDataTable)   ' Concurrency violation: the UpdateCommand affected 0 of the expected 1 records.
            myDataAdapter.AcceptChangesDuringUpdate = True
        Catch ex As MySqlException
            MsgBox("MySQL Error: " & ex.Message)
        Finally
            Conn.Close()
            Conn.Dispose()
        End Try
    End Sub
End Class

What I have tried:

I can't see anything wrong with the code, maybe not the best way to code this but since it works on one database and not the other, it leads me to think there is something 'odd' with the database/MySQL setup itself?

Any pointers in the right direction, greatly appreciated, if I loose anymore hair I'll be Homer Simpsons twin! ;)