You will get this error whenever you try to update a list item.
“The security validation for this page is invalid. Click Back in your Webbrowser, refresh the page, and try your operation again.”
The solution will be working fine. And if you try running the same application after some time it will give the same error. If you rebuild the solution and GAC it again, the application will work fine. Check this post also
You may get this error because you are updating a list item by object model.To overcome this
- Goto CentralAdmin ->Application Management -> Web Application General Settings
- Select the appropriate web application
- Under Web Page Security Validation section select change Security validation to off.
Now you can see the application running properly.
But aware this is not a suggested solution.