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To fix the issue, you will need to enable cookies from PICSWeb in your internet browser. Instructions are available on enabling cookies for various browsers:
Copying the URL after Redirecting
Once you open the URL from the WebForm email, you will be immediately redirected to the relevant form. This means that if you try and open the form using the URL in your browser, you will no longer be using the correct link, resulting in the error message above. To avoid this, make sure you only use the link attached to the button in the original WebForm email.