How to resolve “This is an invalid webresource request” error in ASP .Net
Not really sure how that happened but try adding this code to your web config
And then in your IIS, under Machine Key for the website, we have Encryption Method = SHA1Decryption Method = DES
make sure all the checkboxes for Validation key and Decryption key are unchecked.Note that "xxx" and "yyy" are in the key fields.
After making this change, you may need to recycle your app pool, and clear browser caches.