I am facing this error from last two days, I tried so many resolutions to resolve this problem.
I had tried to know the reason of this error but, unfortunately I am not able to reach the cause of this error.
But, I had find a solution of this error.
Update your web.config with following attributes.
<pages validateRequest="false" enableEventValidation="false" viewStateEncryptionMode ="Never" enableViewStateMac="false">
Download Sample Web.config