Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster.

Hi 
I have this error
and I did the following on my web.config (I added <pages enableViewStateMac="false" />) on web.config
<system.web> <compilation debug="true" targetFramework="4.5.2" /> <httpRuntime targetFramework="4.5.2" /> <pages enableViewStateMac="false" /> </system.web> I had no luck, it didn't solved my problem .
Any help, please?
Thank you
mario