This is common error generally working with UpdatePanel.
On your screen you see message "Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster."
You can fix it in two ways, setting in web.config or in page it self.
<pages enableEventValidation="false" viewStateEncryptionMode ="Never" />
Or in page you write following line in @Page directive.
<%@ Page EnableEventValidation="false" ViewStateEncryptionMode="never" ...