The Validation of Viewstate MAC failed error commonly occurs when an ASP.NET application developer uses the Membership, Roles and/or Profile Providers included with the .NET Framework. The usual scenario is the developer creates the application on their local machine and stores the project files in a local directory. When the developer copies or publishes the project files to another local directory or to a remote server, the login system doesn’t appear to function properly.

The solution is to (more…)