Updating row of a dataset

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VB

dataset

I am fetching selected row of a datagridview to textboxes and trying to update the row using dataset created to populate the datagridview.
I am NOT finding the row in the dataset even though the value of textbox (corrosponding to the PK column in the table) exists in the table row.
What am I doing wrong? I get NullReferenceException (on the statement marked in the code below). Please help.

My code is:

=============================================================
Private Sub btnUpdateClient_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnUpdateClient.Click
Dim tblTemp As DataTable
tblTemp = ds.Tables("Clients")
Dim editRow As DataRow

Dim s As String = txtId.Text

editRow = ds.Tables("Clients").Rows.Find(s) 'Val to find MUST be a PK in table

editRow.BeginEdit() <<= Getting error here

editRow("ClientName") = txtName.Text
editRow("ClientAddress") = txtAddress.Text
editRow("City") = txtCity.Text
editRow("State") = txtState.Text
editRow("Zip") = txtZip.Text
editRow("ClientPhoneM") = txtPhLL.Text
editRow("ClientPhoneLL") = txtPhM.Text
editRow("ClientNotes") = txtNotes.Text

editRow.EndEdit()

Dim oledbCmdBuilder = New OleDbCommandBuilder(dataadapter)
dataadapter.Update(ds, "Clients")

MsgBox("Database Server updated successfully" & Chr(13) & "Check table to see changes.")

==================================================

The Exception and the stack trace is as below:
System.NullReferenceException was unhandled
HResult=-2147467261
Message=Object reference not set to an instance of an object.
Source=AdvantechClient
StackTrace:
at AdvantechClient.Form1.btnUpdateClient_Click(Object sender, EventArgs e) in C:\AdvantechClient\AdvantechClient\Form1.vb:line 157
at System.Windows.Forms.Control.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ButtonBase.WndProc(Message& m)
at System.Windows.Forms.Button.WndProc(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
at System.Windows.Forms.Application.Run(ApplicationContext context)
at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.OnRun()
at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.DoApplicationModel()
at Microsoft.VisualBasic.ApplicationServices.WindowsFormsApplicationBase.Run(String[] commandLine)
at AdvantechClient.My.MyApplication.Main(String[] Args) in 17d14f5c-a337-4978-8281-53493378c1071.vb:line 81
at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadHelper.ThreadStart()
InnerException: