Oracle Database Discussions

Hi!
I need to get the following configuration working:
Linux Server (CentOS 5 32 bits) with Oracle 11.2.0.1.0
Windows Server 2003 SP2 32 bits.
On the windows server I have created a user called oracle, who is member of oinstall and dba groups. (On Linux username, and group membership is the same).
After that, I share a directory on D:\data_pump (I gave the full control of directory to oracle user). I mount the windows share on my linux as follows:
mount -t cifs //winserver/data_pump /u04/oradata/data_pump -o user=oracle,password="pass",uid=oracle,gid=oinstall
As the linux oracle user I'm capable of create and edit files, but:
I connect to my database, create the directory called DATA_PUMP pointing to my cifs mount point, and, after that, I issue the following expdp sentence:
expdp system DIRECTORY=DATA_PUMP DUMPFILE=test4.dmp LOGFILE=test4.log FULL=yes

And I get the following error:
ORA-39006: internal error

Looking at expdp log I found the following information:
ORA-39097: Data Pump job encountered unexpected error -31643
ORA-39065: unexpected master process exception in FILE
ORA-31643: unable to close dump file "/u04/oradata/data_pump/gaston4.dmp"
ORA-19510: failed to set size of 1 blocks for file "/u04/oradata/data_pump/gaston4.dmp" (block size=4096)
ORA-27045: unable to close the file
Linux Error: 5: Input/output error
Additional information: 4

Do you have any suggestions?

Thanks in advance.