Cannot decrypt password error

November Happy Hour will be moved to Thursday December 5th.

When trying to use ActiveDirectoryMembershipProvider with Community via:

I get the error below. Any ideas on where I should look?

Cannot decrypt password

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.InvalidOperationException: Cannot decrypt password

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:

[InvalidOperationException: Cannot decrypt password]
   EPiServer.Common.Security.HMACPasswordProvider.DecryptPassword(Byte[] ciphertext) +46
   EPiServer.Common.Security.User.get_Password() +40
   EPiServer.Common.Web.Authorization.MembershipProvider.GetPassword(String username, String answer) +73
   System.Web.Security.MembershipUser.GetPassword() +106
   EPiServer.Common.Web.Authorization.Integrator.SynchronizeUser(MembershipUser membershipUser, String password, Boolean enableCreateNew) +669
   EPiServer.Common.Web.Authorization.IntegrationHttpModule.SynchronizeUser(String userName, Boolean createNew) +74
   EPiServer.Common.Web.Authorization.IntegrationHttpModule.context_AuthenticateRequest(Object sender, EventArgs e) +209
   System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +136
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +69