ORA-39000, ORA-39143 ORA- 31619 invalid dump file in datapump

Today i am tired to export  one schema (hr) from the one database  into another database  ( import schema )
so i created one directory which is called "ram"
grant read and write access to  the system user ,then i started export the schema (hr) from production  while i did the export of hr schema the job was successful after that i did import schema like below

expdp :

C:\>expdp system/oracle directory=ram schemas=hr dumpfile=hr.dmp logfile=hr.log
......
......
Dump file set for SYSTEM.SYS_EXPORT_SCHEMA_02 is:
  C:\datapump\HR.DMP
Job "SYSTEM"."SYS_EXPORT_SCHEMA_02" successfully completed at 13:23:40


impdp:

C:\>impdp system/oracle directory=ram remap_schema=hr:scott dumpfile=HR.DMP logfile=hr.log



it through an error like below
.



ORA-39001: invalid argument value
ORA-39000: bad dump file specification
ORA-31619: invalid dump file "C:\datapump\hr.dmp"
ORA-27091: unable to queue I/O
ORA-27070: async read/write failed
OSD-04006: ReadFile() failure, unable to read from file
O/S-Error: (OS 38) Reached the end of the file.

cause of the problem:

The data pump export job was showing successful but the reason(our impdp ) can't  able to read the dump file properly or we doesn't give the read and write access to directory "RAM" on the "system" user

solution:
 
1)give the read ,write access to system user for the RAM directory
2) delete the existing export of (hr) schema dump file and create new one then do the import it is working fine