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when i exported this schema .. this error appear
can you help me to understand why this error appear?

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Connected to: Oracle Database 10g Enterprise Edition Release 10.1.0.2.0 - Production
With the Partitioning, OLAP and Data Mining options
Export done in AR8ISO8859P6 character set and UTF8 NCHAR character set

About to export specified users ...
. exporting pre-schema procedural objects and actions
. exporting foreign function library names for user WAPT
. exporting foreign function library names for user MTCSMS2RADIO7
. exporting PUBLIC type synonyms
. exporting private type synonyms
. exporting PUBLIC type synonyms
. exporting private type synonyms
. exporting object type definitions for user WAPT
. exporting object type definitions for user MTCSMS2RADIO7
About to export WAPT's objects ...
. exporting database links
. exporting sequence numbers
. exporting cluster definitions
EXP-00056: ORACLE error 4021 encountered
ORA-04021: timeout occurred while waiting to lock object
ORA-06512: at "SYS.DBMS_METADATA", line 1511
ORA-06512: at "SYS.DBMS_METADATA", line 1548
ORA-06512: at "SYS.DBMS_METADATA", line 1864
ORA-06512: at "SYS.DBMS_METADATA", line 3707
ORA-06512: at "SYS.DBMS_METADATA", line 3689
ORA-06512: at line 1
EXP-00000: Export terminated unsuccessfully
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really i need a solution for this error ..
this error resolved by restart the machine ,
but i cannot do that every time ,
it is a server 24h/7days .

anyone can help me how to resolve this problem without restart the machine ..

i used (consistent=y) but still the problem occurs.

thnx to all ,

Stop remote agents reporting into Grid Control, in addition to the Grid Control's agent, before exporting or applying the 10.1.0.4.0 patchset ( 3731593 )(upgrading).