[SOLVED] Error installing along side Windows 10

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FYI: I know all (???) about the boot manager. I use it to boot from a Windows 7 USB stick quite often.
I was able to get to the information on the Windows partition(?) by right clicking on the "removable volume" icon on the Linux Lite desktop and choosing to mount the volume.
My computer is a Dell Optiplex 790 with a 500 Gb SSD. The BIOS is version A21.
The hold right shift key while booting did nothing (no UEFI).