I wanted to answer the question in this topic, but found that it was already closed, so I am making a new topic for this in this board. I hope that's okay.

 

The solution to clear the ePSA Event Log was first posted in this topic, but you may get an error message that you do not have permission to delete the file. I found out through this page that some UEFI variables cannot be deleted because they have the immutable attribute set. Simply unsetting this attribute allows you to delete the file representing the variable.

 

Basic instructions:

Start your system in UEFI mode from a live medium such as an Ubuntu USB stick.

Open the terminal.

Use the following commands in succession:

• sudo su
• chattr -i /sys/firmware/efi/efivars/DIAGEEPROM_VAR-XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX
• rm /sys/firmware/efi/efivars/DIAGEEPROM_VAR-XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX

Where the Xs are numbers specific to your system (tip: use tab to autocomplete the filename).

Close the terminal and reboot.

 

I hope this information is useful to someone.