I am not sure what is your exact setup, but most probably you should not use AutoLoad=true and turn it on once you have authenticated the user. If AutoLoad is false, RadDomainDataSource will not try to load unless told to do so by calling its Load method.
On the other hand, how would you go about solving the problem if you were using the stock MS DomainDataSource? If you know the answer to this question, I guess it will be the same with RadDomainDataSource, since the two controls have one and the same internal logic. In other words, this might really be a WCF RIA Services problem/question and not specifically a Telerik control one.
I hope this helps.
All the best,
the Telerik team
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