In my case, I'm upgrading to Ubuntu 12.04 LTS from Ubuntu 11.10. The machine is hosted at Linode who compiles the netfilter modules into their kernels.
Error occurred during do-release-upgrade and here is the same error from apt-get install iptables-persistent:
Setting up iptables-persistent (0.5.3ubuntu2) ...
dpkg: error processing iptables-persistent (--configure):
subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
iptables-persistent
E: Sub-process /usr/bin/dpkg returned an error code (1)
I traced this to /var/lib/dpkg/info/iptables-persistent.postinst and the following modprobe:
modprobe -q iptable_filter
If iptable_filter is not available as a module, modprobe returns a non-zero exit status which halts execution of the postinst script.
From "man modprobe" in the -q section:
However, it will still return with a non-zero exit status. The kernel uses this to opportunistically probe for modules which might exist using request_module.
Changing the modprobe calls to trap the errors using " || true" worked for me:
modprobe -q iptable_filter || true
Status changed to 'Confirmed' because the bug affects multiple users.