We do not support 3rd party plugins here. You would want to talk with the author that you got the plugin from.
But in the meantime you can get your instance working again by disabling the plugin.
Open your mysql command prompt or favorite 3rd party DB editor and either view the ost_plugin and set the plugin isactive to 0 (disabled) or customize and run the following the query:
UPDATE ost_plugin SET isactive=0 WHERE name='osTicket Reports';
I also run this plugin where I work. 🙂 [note I haven't upgraded in a bit though]