If you add or remove a trusted domain, and either set the date on the 'problem' computer to a future or previous date, even if you subsequently fix the date, your logon dialog will not show the change to the trusted domain.
To work around this problem, use Regedt32 to navigate to:
Select the Dcache value name in the right hand pane and press Delete.
Select the DcacheUpdate value name and Delete it.
After you restart your computer, the domain list will be rebuilt.