ayesjm osticket version 1.9.15
This version of osTicket is end of life and has not been supported for quite some time.
If you downloaded the plugin from the osTicket website then it is likely only intended for use with a more contemporary version. You will need to disable the plugin on your site.
Since you cannot log in you will need to do this in the Database directly. You can use your favorite 3rd party SQL editor (like MySQL WorkBench or HeidiSQL) and look at the ost_plugin table. Locate the entry for LDAP Authentication and Lookup and set isactive to 0.