If you see such a problem after the Business Process Manager add-on installation try to follow these steps to fix it by yourself.
If you don't have access to the options below, contact your Jira administrator.
Go to Settings > Issues > Fields > Field Configurations. Delete BPM Field Configuration. Then in the sidebar go to Field Configuration Schemes and delete BPM Field Configuration Scheme.
Go to Settings > Projects and delete the BPM Templates project. Also, delete it from Trash.
Uninstall add-on by following this instruction.
Now reinstall Business Process Manager add-on by going to this page and start testing tool to fulfill your business needs
If you are still having problems contact support@saasjet.com!