Why does FormsAuthentication.Decrypt crashes when moving to another Server

The reason why the encrypted data couldn’t be decrypted on another machine is because the validation key in the original machine’s machine.config is set to AutoGenerate. This means that the generated keys are unique to each machine. A better solution will be to specify the validation key, so you can decrypt it across any machine with the same validation key.
For more details on solution refer following article :

• Microsoft Knowledge Base Article – 313091
• Microsoft Knowledge Base Article – 312906