Hi,
SharePoint would search for the two-way trusted domains automatically, I suppose your issue happened on a one-way trusted domain.
If so, you need to use Peoplepicker-searchadforests: Stsadm property (Office SharePoint Server) to configure on your sites before SharePoint can search for the users.
Hope the information can be helpful.
-lambert
Sincerely,
Lambert Qin | Microsoft TechNet Managed Forum Support
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