This may need to be fixed in GRUB(2), and how the kernels are complied. Not just one.
If GRUB can get the correct UDMA mode from the drive, it needs to do that; when it otherwise gives a "Invalid Magic Number", error.
The kernels need to be compiled with options like the older kernels(that just worked). Perhaps referencing UDMA.
This may need to be fixed in GRUB(2), and how the kernels are complied. Not just one.
If GRUB can get the correct UDMA mode from the drive, it needs to do that; when it otherwise gives a "Invalid Magic Number", error.
The kernels need to be compiled with options like the older kernels(that just worked). Perhaps referencing UDMA.