The requested search root domain.local/Users’ is not within the scope of this operation. Cannot perform searches outside the scope ‘child.domain.local’.

2007 = $AdminSessionADSettings.ViewEntireForest = $true

2010 = Set-AdServerSettings -ViewEntireForest $True

or use –ignonreDefaultScope on the command if applicable, i.e.

get-mailbox –ignonreDefaultScope

http://technet.microsoft.com/en-us/library/bb124527.aspx

How can this be made permanent ?

you could add it to the personal EMS startup

Default Location:

My Documents\WindowsPowerShell\profile.ps1