I wasn't sure where to put this question, but hopefully this is an OK place.
I've been getting a few errors over the last two days about "Validation of viewstate MAC failed." with the login return URL.
E.g.
Page Load Exception
RawURL: /Login/tabid/697/Default.aspx?returnurl=%url_removed_for_privacy.aspx
AbsoluteURL: /Default.aspx
AbsoluteURLReferrer: https:/mydomain.com/Login/tabid/697/Default.aspx?returnurl=%url_removed_for_privacy.aspx
UserAgent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0; NP10)
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke.SqlDataProvider
ExceptionGUID: 06bc6e83-f6b7-4348-8877-8c00eb5f08b0
InnerException: 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.
Message: DotNetNuke.Services.Exceptions.PageLoadException: 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. ---> 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. ---> System.Web.UI.ViewStateException: Invalid viewstate. Client IP: 10.5.61.86 Port: 50435 User-Agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0; NP10) ViewState: X3zeplQoGADSBMG2XXJYujFEdJZQp/fcSs+ladfvuYi/ykQuDIPrP04g+cnS0IgjZdukX7vkI211CSr8+oWHYzVb45CFp+YCezEbBv7NsISlr1alZdxF7qIpn1gh0Nd7YkYIue68Y+bkRAkjfwYU0oMZLXM5LaYHR6ijwRKBU0gnT82ZXMgDg+7hZre9HLanG9NV45rmxsx161lAH03nQ/F7KZtmqJslCMqfXrpFjUl9cP+o0gwxsv+2jUNOu6LDrP6E/Uw89ZhaOBgW5r8+S8ELudrGHOdgbyTlh+DHKNJtzR7tLXv99lAqdgxomeNBM81yl6ru+mf8m3Z+BtmeCUYus+lT2sSQ53BOKVPWwUKBt+FPgMlvku0SM9s1jkP5sUWt/NpkZHIY5XKGp22+6ymZyjO5izAwr4xiCL+rftE7AvpzJQ/WouBzMwcP41gkV+zRsGqqj3KIkQEI3FIu5SbjegRQbpIuFLQOj6CTxjgRiuFpY1fpRf8rpKZgL6wc46ItikLr3zZYd3T02S0L07EuX454szCP7u/vPYQVdvPrcS6ELmnJVEi1iwteOuVIwetvcfj71ge0Hj/mnC8Qa9zsMJmUVeZHscZM+Sw072kIcbhCPWF8gOyquqTX9/wFGHUt5gqi2g8ES1RDfmyzAmZICVWv8msQ/YQKHPvnm8iJVRc08QIfaZtyhsyxeDvuDLkcy8+sSQMAxRHJnZIkxda2GrdL72qGrXJgOlkSLWKvb6ApssjAobYrycNcimh6kLHIDFPSzmYiGd34T3VX9+LqWg8VzAtdU2zLy5AVC0Jm8OLqETY8AKeHjkjvCgc+b25IY+0rjpEWu15pLRBzwgjPXHdbjpv2kc//8YuK1DP71z... --- End of inner exception stack trace --- at System.Web.UI.ViewStateException.ThrowError(Exception inner, String persistedState, String errorPageMessage, Boolean macValidati ) at System.Web.UI.ObjectStateFormatter.Deserialize(String inputString) at System.Web.UI.Util.DeserializeWithAssert(IStateFormatter formatter, String serializedState) at System.Web.UI.HiddenFieldPageStatePersister.Load() at System.Web.UI.Page.LoadPageStateFromPersistenceMedium() at System.Web.UI.Page.LoadAllState() at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) --- End of inner exception stack trace ---