[kiwidude]

@vladcr - I am not sure what else to suggest, though your latest post intrigues me a little.

1. When you installed the plugin, did you get asked with a dialog about which menu/toolbar to add the plugin to?
2. If so, which did you choose, and did it appear on there when you restarted Calibre?
3. If it does not appear, if you start Calibre using calibre-debug -g do you see an error (or is that same error you see above)?

What I find interesting about your post above is if you do get to the point of being asked what menus/toolbars to add the plugin to when you install the plugin. If it does that, that means it has successfully "started up" the plugin from the zip file, because it needs to start the plugin to get information about which toolbars/menus the plugin is allowed to be added to if any. That it might load the plugin correctly at that point, but not after restarting Calibre, perhaps says something...

EDIT: I just realised you said you did this with 0.7.46. This would be before we added the feature to Calibre to prompt you for a menu/toolbar while installing a plugin. So not so meaningful after all. If you uninstall the plugin, upgrade to 0.7.50, then install the plugin, let me know what happens when you click install...