Software :: BzImage OK But Vmlinuz Not Booting

I use Linux (Gentoo) since many years. I always used gentoo-kernels which I configured and compiled. Once it was done I usually got a "vmlinux"-file and a "bzImage"-file. I always used to copy the "bzImage"-file to my boot partition and I configured Grub accordingly and everything was fine.

Last week I compiled in my VM not only gentoo-kernels, but as well a xen-kernel (for my domU). Once it was done compiling the Xen-kernel (used the usual command "make -j2 && make modules_install") it didn't generate a "bzImage"-file, but a "vmlinuz" file. I therefore took the vmlinuz-file, copied it as usual to the boot partition and configured Grub to use that one, but with this time Grub doesn't want to boot and returns each time the error

Code:
Error 13: Invalid or unsupported executable format
Press any key to continue...

I tried with both "vmlinuz" and "vmlinux" but neither worked. I have no clue what I should to - should I try to somehow generate a "bzImage" (tried "make bzImage" after a "make clean", but it tells me that it doesn't find any bzImage to create), convert vmlinux/z to bzImage or make Grub somehow boot using vmlinuz?

Are there any "tricks" to make Grub boot using a vmlinux/z?

I can say that it's not a problem of the partitioning or setup config in Grub, as in the same grub.conf I have other 2 kernels (bzImage) which boot without problems only the config section that has to do with the vmlinuz/x doesn't want to boot.