1) check if your user have the correct privilege (directory), if not:

GRANT READ,WRITE ON DIRECTORY <your_directory> TO <your_user>;

2) check the permissions of oracle user at OS, and who is the owner of this directory:

ls -l <directory>

*if your user is the owner, he could modify it with "chmod XXX <DIRECTORY>", if (for example) root is the owner, you can't write on it unless he modifies the permissions on that directory (again with chmod):

http://superuser.com/questions/208606/how-to-change-file-permissions-for-a-directory-in-one-command

3) if you can't modify the permissions of this directory, create a new directory in other path (where your user can write).

Hi,

You can not do it by database side, you have to choose the alternate from OS side. one method you can use setfacl 

check  with your system admin who provide you the command  to access on directory  so you can read write that files.

HTH

What are the permissions on the dumpfile after it has been created? Set umask to 022 if this has not already set to.

What are the permissions on the dumpfile after it has been created? What other files you are talking too?