Setting the correct search scope for the people picker:
- stsadm -o setapppassword -password xxxxxx
- stsadm -o setproperty -pn peoplepickser-searchadforests -pv "domain:first.com;domain:second.com,domain\user,password" -url http://sharepoint2010/
First.com domain trusts users from second.com. For the people picker to find users in the second.com domain a valid user in second.com domain has to be provided. Because we provide a user name and password we first have to set the password encryption key.