Hi,
I think that i’ve found a bug Notes 8.5.1 - Search functionality.
Try reproducing it : Go to Preferences → Search and uncheck “Enable History” checkbox. Now come to the Search box on the right of the toolbar and select “All Mail” as your Search Scope. Now type any word and press Enter. Notes will display an error message “Search application has encountered a problem”.
Or is it happening only to me??? Any ideas???