“Validation of viewstate MAC failed. If this application is hosted by a Web Far…”

Question

i am facing the dreaded:

Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that configuration specifies the

Answer 1

At my site, this meta tag were causing the error:

I have a dropdown, I update on another dropdowns changed selection. So when the postback happened (dropdown #2 changed index), I got the exception.

I've tried everything else from applying machinekey to web.config and setting theese attributes at the page

EnableViewState="false" EnableViewStateMac="false"