USB Boot Capability Mysteriously Vanished from BIOS Setup Menu - how can I get it back?

I have a PowerEdge 2900. The ability to boot from the USB has mysterious disappeared from the BIOS setup menu. It seemed to disappear after I attempted to install Ubuntu Server from a bootable USB stick.

The hardware manual says that there should be a Setup menu item “USB Flash Drive Emulation Type” listed sequentially after the Setup menu item “Boot Sequence”. But instead of “USB Flash Drive Emulation Type”, it says “Boot Sequence Retry”. I upgraded the BIOS to 2.6.1 hoping that the “USB Flash Drive Emulation Type” menu item would reappear but it didn’t.

I also checked in “Integrated Devices” and confirmed that “Users Accessible USB Ports” is set to “All Ports on”.

What do I need to do to get the ability to boot from USB back?