Outlook 2007 – Search subfolders in additional mailbox

I have recently setup a laptop for a user which uses a additional mailbox in Outlook 2007. He usually runs a report on the inbox of his shared mailbox which contains subfolders, by running an advanced find (ctrl+shift+f). However the search subfolders tick box, found by clicking the browse button, is greyed out. Now my question is, why did this work before on his old desktop?