TOPIC: How to re-install the plugin when it's not working

I think, that when we delete all files and database items and after that re-install it, it will work fine.
On other Joomla sites, your plugin works very good, only on one (older and updated) site it's behaving this way.

You have problem with language files.
Are you sure than you don't have files?:
- administrator/language/en-GB/en-GB.plg_content_mavikthumbnails.sys.ini
- administrator/language/en-GB/en-GB.plg_content_mavikthumbnails.ini
- administrator/language/<your language>/<your language>.plg_content_mavikthumbnails.sys.ini
- administrator/language/<your language>/<your language>.plg_content_mavikthumbnails.ini