HERE as Sony added in a MAC check, but after reading the error part I quoted above it seems like you are correct... it might be something new.
PS: I think I read something that said the French site PSPGen have found that Sony now detects CFW on the PSP... if I can find the link I will add it below.
Edit: I believe this is the link, but probably not the issue in your case as the translated title reads: "The first game that detects Custom Firmware is here!" http://www.pspgen.com/premier-jeu-qu...te-188285.html
I was going to say did you see