ORA-00372
ORA-00372: file string cannot be modified at this time
Cause: attempting to modify the contents of a file that cannot be modified. The file is most likely part of a read only tablespace but may be in the process of going offline, or the database may be in the process of closing.
Action: check the status of the file and its tablespace


there is no such things as 'default user01.dbf'

what EXACTLY are you doing and what did you do to get there