UDI-00052: incorrect Data Pump client for operation: EXPORT
                                                 Last update (2012-06-19 23:03:01)
                                                                                                                   Date added (2012-06-19 22:49:04)

Summary
You are trying to attach a data pump job running but you get the error:
UDI-00052: incorrect Data Pump client for operation: EXPORT

for example is running

expdp system/**** FULL=y DIRECTORY=datapump DUMPFILE=full%U.dmp LOGFILE=full.log

and trying to attach
SQL> SELECT * FROM DBA_DATAPUMP_JOBS;

OWNER_NAME    JOB_NAME              OPERATION     JOB_MODE   STATE       
------------------------------ -----------------  ---------- -------
SYSTEM        SYS_EXPORT_FULL_01    EXPORT        FULL       EXECUTING 

$ impdp system/**** attach=SYS_EXPORT_FULL_01

Import: Release 11.2.0.3.0 - Production on Tue Jun 19 22:40:41 2012

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Connected to: Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
With the Partitioning, OLAP and Data Mining options
UDI-00052: incorrect Data Pump client for operation: EXPORT

BE CAREFUL!!! you are running an EXPORT (expdp), you cannot attach with IMPORT(impdp) the export job!

Obvious the right command is :
expdp system/**** attach=SYS_EXPORT_FULL_01