Standard ASP.NET Role, Membership and Profile providers cannot work properly in Sitefinity 4.0 BETA, because of a missing implementation in our wrappers that "converts" all data. The error you get is called from Enterprise library due to issues caused by our code. We will ensure that there will not be issues with standard providers for the RC of Sitefinity. I am sorry if this have caused any inconvenience for you.
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