[SOLVED, most probably] Grub problems after reinstalling Linux Mint 18.2 (from dual boot with Windows to LM only)

[BG405]

In the Security menu there should be an option "Erase all Secure Boot setting:". After doing this redo the "Select an UEFI file as trusted for executing:". Note that I have Secure Boot enabled on the Acer ES1 and this is probably needed in order to perform the above.

[kramarov]

In the Security menu there should be an option "Erase all Secure Boot setting:". After doing this redo the "Select an UEFI file as trusted for executing:". Note that I have Secure Boot enabled on the Acer ES1 and this is probably needed in order to perform the above.

I'm sorry i'm answering a whole week later.. was extra busy at work after the holidays..

Thank you VERY much for the advice. It helped, no more error messages
Yes, superuser password needs to be set and Secure boot enabled. I only have to add that i had to F9 after erasing the settings and then re-enter the bios to set the trusted files (first time i tried to do both things without exiting and got "No bootable device" )

I'd like to mark this as "solved" now; the only thing that confuses me is that the grub menu looks somewhat funny:


(the highlighted line is "advanced options")
I selected grubx64.efi and shimx64.efi as trusted , the 3 other files appeared without me asking. I understand more or less what they are for, but are they really needed there?

One more screenshot:


Is everything ok here?
Just want to make sure i haven't messed it up again (before i do anything important like kernel update or dual boot etc.)

[BG405]

Looks OK to me; I'll check my EFI machine later just to be sure.