El Capitan 10.11.2 In Safari 9.0.2, I open a web page. I go to File/Export to PDF. I make the pdf upon the desktop. I IMPORT this pdf into iBooks 1.4. Then trash the pdf on my desktop. Go to Finder/Empty Trash. But get the message "Operation can't be completed . . ." I FORCE QUIT (Apple+Option+Escape) all apps+ relaunch the Finder. Still the pdf cannot be emptied from the trash. I must reboot to empty the trash. Why????? What is running to prevent a created pdf from being emptied?