Executing procedures from the dbms_java Oracle PL/SQL package may result in a strange IdNotFoundException like:

ORA-29532: Java call terminated by uncaught Java exception: oracle.aurora.vm.IdNotFoundException: user : user or role id does not exist

This is very common when granting

call dbms_java.grant_permission('user', '', 'C:/MyFolder/ora-pgp-1.1.0.jar', 'read');

If you experience such error try changing the user(schema) name to Uppercase.