ORA-31694: master table "SYSTEM"."SYS_IMPORT_SCHEMA_01" failed to load/unload
ORA-02354: error in exporting/importing data
ORA-39774: parse of metadata stream failed with the following error:
 LPX-00217: invalid character 0 (U+0000
ORA-39014: One or more workers have prematurely exited.

Export database:  UTF8
Import database:  AL16UTF16

Execute the following commands in sqlplus connected as "/ AS SYSDBA":

       SHUTDOWN IMMEDIATE;
       STARTUP MOUNT;  
       ALTER SYSTEM ENABLE RESTRICTED SESSION; 
       ALTER SYSTEM SET JOB_QUEUE_PROCESSES=0; 
       ALTER SYSTEM SET AQ_TM_PROCESSES=0; 
       ALTER DATABASE OPEN; 
       ALTER DATABASE NATIONAL CHARACTER SET UTF8;
       SHUTDOWN IMMEDIATE;