[apt-offline-devel] v1.5 not working: apt_pkg.init_config() global name apt_pkg is not defined

[tigusoft.build]

On Debian 8 (amd64), I have apt-offline version 1.5 (according to dpkg -l and to the program with -v).

When I try to use it with any options, I get error:
...
... in main()
... in main
... in setter
... in Update
.... AptOfflineCOreLib.py line 1623 in __PythonAptUpdate
apt_pkg.init_config()

NameError: global name 'apt_pkg' is not defined.

When I run e.g:
apt-offline set test.sig

my /etc/apt/sources.list file containd a cdrom line, like
deb cdrom:[Debian......]/ jessie contrib main
that I now commented out (after trying apt-offline first)

in next lines is contains a 
deb http://security.debian.org/ jessie/updates main contrib
deb-src http://security.debian.org/ jessie/updates main contrib

this are all lines (besides comments).

Please tell me how to fix this (or how to provide more information)