unique constraint (%s.%s) violated

Today while trying to insert a row into a table (have 500000 rows approx) I got the following error :-  

ERROR at line 1:

ORA-00001: unique constraint (%s.%s) violated  

I am using Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - 64bit.  

I am not violating any constraint while inserting this row.  

Any idea about why I am getting this and How to resolve this error ?  

Thanks in Advance

Krishan  

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