[galaxy-user] How to delete multiple items in libraries?

Hello everyone In the admin panel > Manage data libraries section I have an issue with deleting datasets. When I click on each dataset's triangle menu and ask for deletion, everything is fine. But whenever I select datasets and ask for deletion with the drop down menu at the bottom of the page, Galaxy tells me I don't have the rights to delete them. I get the following message: "You are not authorized to delete any of the selected datasets." Did I miss anything? Thanks, L-A