Upgrading SLES 12.5 to 15.5 Error

m trying to upgrade a VM server from sles 12 SP5 to 15 through a boot from a virtual CD ( [SLE-15-SP5-Full-x86_64-GM-Media1.iso] But im getting this error after boot, and initial load:
Any pointers would be appriciated

Error
Internal error: private constant Y2Package ProductUpgrade MAPPING refrenced.

So you’re booting from the virtual media to do an offline upgrade but at what point does it display the above error? Are you able to choose Upgrade from the boot menu (after the welcome screen)?

Yes, exactly. I get through the welcome screen, choose upgrade, and once it reaches “performing upgrade” i get that error. If i then chose “abort” it goes back to simple install upgrade. . it tries once more and then i get , i brifely see the "looking up local registration servers " before it pops up.