How do I see if a textbox contains this OR contains that properly?

[Louix]

I have this code driving a validator:

If TextBox1.Text.Contains(".urw") Or TextBox1.Text.Contains(".URW") = False Then
            TextBox2.AppendText("Input file is not a valid. Please try again.")

But I also have an opposite one under the "true" condition.

However, no matter what I do, my utility only validates ".URW" correctly and not ".urw".

Does anybody know why?