[2005] Code warnings

[wiadus]

Hi I have this code and function which shows no warnings in vs 2003 but showing warnings in vs 2005. This code shows the following warning(Access of shared member, constant member, enum member or nested type through an instance; qualifying expression will not be evaluated.)

   Private Sub btnDelete_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnDelete.Click
        Dim iResult As DialogResult = MessageBox.Show("Delete " & cboUsers.Text & "?", _
        "Confirm Delete", MessageBoxButtons.YesNo, MessageBoxIcon.Question)
        If iResult = DialogResult.Yes Then
            drUsers.Delete()
            cboUsers.Focus()
        End If
    End Sub

This function also show this warning (Variable 'sErrorMessage' is used before it has been assigned a value. A null reference exception could result at runtime.)

   Private Function ValidData() As Boolean
        Dim sErrorMessage As String
        If txtFirstName.Text = "" Then
            sErrorMessage = "Please First Name required"
        ElseIf txtSurname.Text = "" Then
            sErrorMessage = "Please Surname required"
        ElseIf txtUserName.Text = "" Then
            sErrorMessage = "Please User Name required"
        ElseIf txtPosition.Text = "" Then
            sErrorMessage = "Please Possition required"
        ElseIf txtEmployeeNo.Text = "" Then
            sErrorMessage = "Please Employee number reqired"
        End If
        If sErrorMessage = "" Then
            ValidData = True
        Else
            ValidData = False
            MessageBox.Show(sErrorMessage, "Data entry error", MessageBoxButtons.OK, MessageBoxIcon.Error)
        End If
    End Function

The bold words in the codes are underline in my code. Could any one help out. Thanks