I have a ASP.NET 2.0 webpage with 3 server controls: RequiredFieldValidator , textbox , and button .` Button uses OnClientClick to call a JavaScript function for validation using Page_ClientValidate() . This page works fine with Chrome, IE, Firefox, Safari (5.1.7 on Windows). It has stopped working with modern Safari versions - 8.0 in Yosemite and Mobile Safari on iOS 8. I see this exception in the Inspect Element area: "ReferenceError: Can't find variable: Page_ClientValidate" How can this be fixed? Solved This sounds like a duplicate of this problem: iOS 8 / Safari 8 not working with ASP.NET AJAX-Extensions Another solution that modifies the web.config instead of the mozill: ReferenceError: Can't find variable: ValidatorEnable in Safari