Since Debian squeeze doesn’t appear to include pre-built iscsitarget kernel modules, the iscsitartget-dkms must be installed. This is a source package and will install gcc etc to compile. It should compile automatically.
apt-get install iscsitarget-dkms
Here is a list of iscsi related packages I installed on my secondary NAS:
iscsitarget 184.108.40.206-1 iSCSI Enterprise Target userland tools
iscsitarget-dkms 220.127.116.11-1 iSCSI Enterprise Target kernel module source – dkms version
open-iscsi 2.0.871.3-2squeeze1 High performance, transport independent iSCSI implementation
I found this info in a bug report through google after I received a module not found error when issuing a /etc/init.d/iscsitarget restart