Hi !
This is the first time I write to this forum.
I have been working with remastering of 5.0.1 version, everything was alright (remove & add packages), until I decided to make a little change in the Welcome message, replacing "Welcome to Knopppix ...", with "Welcome to Avionix, based on Knoppix ...".
I modified the linuxrc file, inside minirt.gz (uncompress, mount, edit, umount and compress again) and build a new ISO and burn a CD.
After this, system doesn't boot and display an error:

Kernel Panic: not syncing: VFS: Unable to mount root fs unknown-block(1,3)

If I restore the original minirt.gz, everything works well again.
I have been "googling" and applying lot of "recipes" and advices, but I can not solve this problem.
I appreciate your help.

There are the followed steps in details:

mastercopy is the master directory needed for remastering, /working is an example working directory.

cp /mastercopy/boot/isolinux/minirt.gz /working/
cd /working
gunzip minirt.gz
mkdir mnt
mount -o loop minirt ./mnt

Now, I can edit (with nano or vi text editor) and save ./mnt/linuxrc file

umount ./mnt
gzip -9 minirt

cp minirt.gz /mastercopy/boot/isolinux/

that's all

Thanks in advance,
Sebastian.