我们最近将所有站点从一台服务器 (IIS6) 移到了新服务器 (IIS7)，这也涉及更改所有 DNS 记录。但是，在某些网站上，当您在某些页面上进行回发时，您会收到以下错误：
Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that <machineKey> 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 <machineKey> configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster.
起初我认为这可能是网站的传播问题（即它试图回发到旧服务器）。但是，DNS 记录在 2 周前被更改，所以肯定不是这种情况。
为什么会出现这个错误？
值得注意的是，这个错误从未在旧服务器上发生过。