Metadata source plugin - worker.py not found

[ru_cal]

I was trying to create a plugin to get metadata for old Russian books from livelib.ru by editing one of the existing plugins, but ran into some problems.

When I add the plugin to calibre, it shows 2 instances of the same plugin on the settings page. When I click download metadata, the log says that file worker.py was not found. What can be the problem?

This is part of the log:
Traceback (most recent call last):
File "site-packages\calibre\ebooks\metadata\sources\identify. py", line 44, in run
File "calibre_plugins.livelib.__init__", line 238, in identify
ImportError: No module named Livelib.worker