I created a live USB stick from downloaded Manjaro Xfce 26 full live ISO from the Manjaro website (verified download checksum) using the mkusb tool’s ISO clone function (my main desktop distro is Mint/Cinnamon).
Booting on a 2008 Aluminum Macbook 5.1, I receive the same error message. Nvidia 9400M graphics, for what it’s worth.
Waiting a long time (I went and did other things, not sure exactly how long, but it was more than five minutes when I gave up the first time), I was able to hit enter to clear the message, and the system gave me a login prompt for user “manjaro”, which I was able to log into using password “manjaro”. I was then able to install without issue, and the system has booted from the installation without issue (other than the common Broadcom driver issue for this Macbook).
So: it’s not a show-stopping bug, whatever it is.
I’ll try on a couple of other platforms later with the same USB stick and see what happens (can’t right now, have to go to work).
If those 5,x MBPs are upgraded to 8 GB SDRAM and SSD manjaro will work well. In their original configuration with 2GB and spinner drive I’d look for a different os, perhaps AntiX.