[reboot fail] couldn't find suitable memory target

Hi,

after successfully compiling and installing the kernel sources on the latest Ubuntu desktop version on real hardware, i have the error on boot "couldn't find a suitable memory target".
I followed the steps in the course to create the initial ".config" copying from "/boot/config-*-generic" and "yes" to all the questions about the new kernel configurations proposed before starting the build.

Doing a search it seems that the error is due to an excessive size of initrd.img- * lastest-kernel-ver * and that unnecessary modules should not be included.
It's correct?
I did not find any reference to this part in the course material.

What is the best way to solve this problem?

br