I'm going to try putting
<%@ Page Language="vb" EnableViewStateMac="False"%>
In the page declaration at the top of the page, that seems to be the consensus when I searched on this error.
What is EnableViewStateMac?
Here is what MSDN documentation has to say about EnableViewStateMac:
EnableViewStateMac
Indicates that ASP.NET should run a machine authentication check (MAC) on the page's view state when the page is posted back from the client. true if view state should be MAC checked; otherwise, false. The default is false.
Note A view state MAC is an encrypted version the hidden variable that a page's view state is persisted to when sent to the browser. When you set this attribute to true, the encrypted view state is checked to verify that it has not been tampered with on the client.
More info here.