After producing an iso with simple-cdd and booting it, debian installer throws this error:

No kernel modules were found. This probably is due to a mismatch between the
kernel used by this version of the installer and the kernel version available in
the archive.

If you're installing from a mirror, you can work around this problem by choosing
to install a different version of Debian. The install will probably fail to work
if you continue without kernel modules.

Continue to install without loading kernel modules?

One solution from the documentation and the mailing list is:

$ echo 'export DI_WWW_HOME=default' >> profiles/default.conf

This will force simple-cdd to call debian-cd to the latest daily build: https://d-i.debian.org/daily-images/amd64/daily/

However that may not solve it or you may already had DI_WWW_HOME=default properly configured and suddenly you started to get this error. The latter was my case - I was running simple-cdd for a few days in a row and this error appeared and persisted during a few more days.

So back to the error: there was a mismatch between kernel version and installer. Let’s check versions we have:

# check installer version
$ file $simple_cdd_dir/tmp/cd-build/stretch/CD1/install.amd/vmlinuz

tmp/cd-build/stretch/CD1/install.amd/vmlinuz: Linux kernel x86 boot executable
bzImage, version 4.5.0-2-amd64 (debian-kernel@lists.debian.org) #1 SMP Debian 4.,
RO-rootFS, swap_dev 0x3, Normal VGA

# check kernel version
$ find $simple_cdd_dir/tmp/cd-build/ -name "linux-image-*-amd64*"
tmp/cd-build/stretch/CD1/pool/main/l/linux/linux-image-4.5.0-1-amd64_4.5.1-1_amd64.deb

Notice that installer version was ahead (4.5.0-2-amd64) than kernel version (4.5.0-1-amd64). The solution was to find out the installer version 4.5.0-1-amd64 and update the profiles/default.conf:

export DI_WWW_HOME=https://d-i.debian.org/daily-images/amd64/20160430-00:16

Now here we’re explicitly pointing the installer to the 2016-04-30 build, which was the day before I got the error. Re-run simple-cdd and versions did match:

# installer version is now in 4.5.0-1
$ file $simple_cdd_dir/tmp/cd-build/stretch/CD1/install.amd/vmlinuz
tmp/cd-build/stretch/CD1/install.amd/vmlinuz: Linux kernel x86 boot executable
bzImage, version 4.5.0-1-amd64 (debian-kernel@lists.debian.org) #1 SMP Debian 4.,
RO-rootFS, swap_dev 0x3, Normal VGA

# kernel version is the same - 4.5.0-1
$ find $simple_cdd_dir/tmp/cd-build/ -name "linux-image-*-amd64*"
tmp/cd-build/stretch/CD1/pool/main/l/linux/linux-image-4.5.0-1-amd64_4.5.1-1_amd64.deb

Booting the produced iso and the No kernel modules were found was gone.

Note that the kernel version should be updated in the repositories to 4.5.0-2 in the meantime. Then the kernel version will be ahead of installers and probably will produce the error again. Switching back to DI_WWW_HOME=default should put both versions aligned for awhile.