that's not your firmware.
it's the patch type used by BDEMU.
In multiMAN you decided to use "Hermes" mode as "BD ROM Emulation", so you are on 3.55 with Hermes patch method using Syscall 8 to patch the Bluray access function.
You are certainly already on Kmeaw 3.55
the errors you are having have nothing to do with the firmware.
Did you try deleting your installed Game data? on the XMB, game column, top menu? do it again then:
Did you try to run a permission check on the iso? do it again without the game data installed. Then:
Do not install the game data from the real Disc.
Launch multiMAN, mount the game you want to play,and launch the mounted game.
The installed data should be installed from the iso, not the disc.
Are you sure the "fix" you installed is for your version?
correct game region?
It's not for Trueblue dongle?
The error could be because it's not using the correct encryption key for 3.55
If these games are 3.60 or less, you can make the fix yourself, no need to download it from an unknown source.
if it's 3.72+, then no luck, you have to depend on other team.