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This problem happens when your asp.net application runs on web farms
Adding enableViewStateMac="false" to webform may solve the problem but it's not recommended.
BY IIS 7
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhNUvTdzADmMHdXgfwXT0E_4S9XzzAOF2c50REydcDT7TmrlkJnp3fEihASvjLcuuCoX9DaYesEhqQ0JmMR2gDf4kO1ol8Uik83MW0UlDEFjE0NfGtCagWDad-Kpp9UTb9IGnE_bdHmzLo5/s320/machinekeys_thumb_2.jpg)
Posted on 2:02 AM by Softminer and filed under
IIS
This problem happens when your asp.net application runs on web farms
Adding enableViewStateMac="false" to webform may solve the problem but it's not recommended.
BY IIS 7
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhNUvTdzADmMHdXgfwXT0E_4S9XzzAOF2c50REydcDT7TmrlkJnp3fEihASvjLcuuCoX9DaYesEhqQ0JmMR2gDf4kO1ol8Uik83MW0UlDEFjE0NfGtCagWDad-Kpp9UTb9IGnE_bdHmzLo5/s320/machinekeys_thumb_2.jpg)
<?xml version="1.0" encoding="UTF-8"?> <configuration> <system.web> <machineKey decryptionKey="xx,IsolateApps" validationKey="xxx,IsolateApps" /> </system.web> </configuration>To generate using Power shell use this instruction http://support.microsoft.com/kb/2915218 Copy and paster powershell script into file, while running you may get security error. To remove security try x86 Open C:\Windows\system32\cmd.exe Run the command powershell Set-ExecutionPolicy RemoteSigned x64 Open C:\Windows\SysWOW64\cmd.exe Run the command powershell Set-ExecutionPolicy RemoteSigned and to set back to default powershell Set-ExecutionPolicy Restricted Power shell Execution Policies