Ir looks like you already had a previous version of the plugin installed and either it did not uninstall or upgrade properly or you tried to delete the previous plugin files but did not remove the entry from the database. You will have to manually clean up the files on your server and database before installing again.
You can try to uninstall via the backend Install/Uninstall menu, but this won't work at this point.
To manually remove the plugin:
1. Delete the following files - plugins/forcepasswordchange directory, plugins/forcepasswordchange.php, plugins/forcepasswordchange.xml and administrator/language/en-GB/en-GB.plg_system_forcepasswordchange.ini
2. In the database delete the entry in the jos_plugins table, there should be an entry with name 'System - Force Password Change'. Here's the SQL query I ran to do it:
DELETE from jos_plugins where element='forcepasswordchange' and folder='system';
Let me know if you still need help after trying these steps.
Installation problem
