ORA-29283: invalid file operation, WHEN UTL_FILE.INVALID_OPERATION on Oracle 11gR2

 Dear Oracle,

I got the errors by an unknown chance. It happened on sometimes, and most time were OK.

Oracle database:version 11.2.0.3 at Windows 2008 R2.

ORA-06512: at "SYS.UTL_FILE", line 41

ORA-06512: at "SYS.UTL_FILE", line 512

ORA-29283: invalid file operation

Here my procedure,

...

v_fileName=:to_char(sysdate, 'mmddyyyy_hh24miss')||'.txt';

...

UTL_FILE.FOPEN ('My_mail', v_fileName, 'W',32767);

UTL_FILE.PUT_LINE (file_handle_msg, 'My Review started '||to_char(sysdate,'mm/dd/yyyy hh24mi')||'.');

UTL_FILE.FCLOSE (file_handle_msg);

...

EXCEPTION

...

WHEN UTL_FILE.INVALID_OPERATION

 THEN

 UTL_FILE.FCLOSE (file_handle_msg);