I'm running Lubuntu 12.10 liveCD, persistent install on FAT32-formatted 4GB pendrive (3.2GB casper file - Unetbootin method).
I can install packages, that's cool.
I tried to install alternative kernel but it failed.
Now I have linux-image-3.4.9-rt17-avl2-pae package as 'obsolete'.
It's not installed but whenever I try to install new package or upgrade the system, I get error:

lubuntu@lubuntu:~$ sudo apt-get install aptitude
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following extra packages will be installed:
aptitude-common libboost-iostreams1.49.0 libcwidget3
Suggested packages:
aptitude-doc-en aptitude-doc tasksel debtags libcwidget-dev
Recommended packages:
apt-xapian-index libparse-debianchangelog-perl
The following packages will be REMOVED:
The following NEW packages will be installed:
aptitude aptitude-common libboost-iostreams1.49.0 libcwidget3
0 upgraded, 4 newly installed, 1 to remove and 116 not upgraded.
2 not fully installed or removed.
Need to get 0 B/2,513 kB of archives.
After this operation, 71.1 MB disk space will be freed.
Do you want to continue [Y/n]?
(Reading database ... 145934 files and directories currently installed.)
Removing linux-image-3.4.9-rt17-avl2-pae ...
update-initramfs: Deleting /boot/initrd.img-3.4.9-rt17-avl2-pae
lzma: (stdout): Write error: No space left on device
run-parts: /etc/kernel/postrm.d/initramfs-tools exited with return code 1
/usr/sbin/grub-probe: error: failed to get canonical path of /cow.
run-parts: /etc/kernel/postrm.d/zz-update-grub exited with return code 1
dpkg: error processing linux-image-3.4.9-rt17-avl2-pae (--remove):
subprocess installed post-removal script returned error exit status 1
Errors were encountered while processing:
E: Sub-process /usr/bin/dpkg returned an error code (1)

How to get rid of it? it's not in /boot, it's not in repos.