I have a mid-2012 13” MBP running on 10.12.6 Sierra, which I’ve been trying to update to the latest OS for some time now. Any update that is newer than Sierra throws a “An error occurred while verifying firmware” error.
After removing the CD/DVD drive in order to fit the caddy/bracket, I have swapped the original HDD with Crucial’s BX300 SSD and tried to find an update, but on their official site there are currently no updates for that particular SSD (https://uk.crucial.com/support/ssd-support/bx300-support). I have also installed additional RAM.
Boot ROM Version: MBP91.00D3.B0B
SMC Version (system): 2.2f44
SSD: CT240BX300SSD1 240GB
According to https://support.apple.com/en-us/HT201518 the latest EFI is .B0C, however unable to install that either (requires OSX 10.9). I’m not an Apple expert, but as far as I understand, it’s because High Sierra and above require the disk to be APFS?
I'm thinking of putting the original HDD back in, or using USB and installing High Sierra (and above) on that HDD and then switching back to SSD. Another option is disabling conversion to APFS during installation. Would that work?