Recently I needed to create a CustomValidator inside a GridView. In the end this was relatively straight forward, however I had some problems in my main application. As I could not find any examples of this on the Internet, I am documenting this here. As a proof of concept I created a web page with an UpdatePanel containing a ValidationSummary, a simple GridView and a button. The GridView was populated by an XMLDataSource (for simplicity), and a column template containing two text boxes and a custom...