Datapump not working in RAC environment
I've found the problem.

The doc ID 1597395.1 says:


  The problem occurs when Datapump Export is being performed on a
  multi-node RAC where the dumpfile destination is not shared to all
  nodes for access.  Since multiple nodes will be running the Datapump
  job, ALL nodes must have access to the mount point where the dump file
  will be written.


So I've just used the parameter cluster=n in export to resolve it.