ASP.NET application is not working properly on a Plesk server: Validation of viewstate MAC failed

Symptoms

• ASP.NET application is not working properly, the following error is shown on a website:

  CONFIG_TEXT: Server Error in '/' Application.
  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. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.Web.HttpException: 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...

• The site is running on IIS using .NET Framework 4.0.

Cause

ASP.NET application-related error.

Resolution

Note: This issue is not associated with Plesk functionality since managing ASP applications is a system administrative task.

Refer to the following Microsoft KB article for resolution steps.

As an alternative, reset Virtual Memory Limit:

1. Connect to the server via RDP.

2. Navigate to IIS Manager > <Server_hostname> > Application Pools > example.com > Advanced Settings... and Set the Virtual Limit Value to 0: