Getting error "ORA-29283: invalid file operation" when trying to write to UTL_FILE directory from Toad for Oracle session. (4333358)

Getting error "ORA-29283: invalid file operation" when executing the code below from Toad:

DECLARE
fHandler UTL_FILE.FILE_TYPE;
BEGIN
fHandler := UTL_FILE.FOPEN('/path/example', 'myfile', 'w');
UTL_FILE.PUTF(fHandler, 'Testing');
UTL_FILE.FCLOSE(fHandler);
EXCEPTION
WHEN utl_file.invalid_path THEN
raise_application_error(-20000,
'ERROR: Invalid path. Create directory or set UTL_FILE_DIR.');
END;
/

the complete error message is :

[Error] Execution (1: 1): ORA-29283: invalid file operation
ORA-06512: at "SYS.UTL_FILE", line 536
ORA-29283: invalid file operation
ORA-06512: at line 4

The same code runs fine from SQL Plus from the same computer.