Delta Import failing - DataImportHandler SOLR 4.2

[PeriS]

I have configured the delta query properly, but not sure why the DIH is 
throwing the following error;

SEVERE: Delta Import Failed
java.lang.RuntimeException: java.lang.NullPointerException
        at 
org.apache.solr.handler.dataimport.DocBuilder.execute(DocBuilder.java:266)
        at 
org.apache.solr.handler.dataimport.DataImporter.doDeltaImport(DataImporter.java:451)
        at 
org.apache.solr.handler.dataimport.DataImporter.runCmd(DataImporter.java:489)
        at 
org.apache.solr.handler.dataimport.DataImporter$1.run(DataImporter.java:468)
Caused by: java.lang.NullPointerException
        at 
org.apache.solr.handler.dataimport.DocBuilder.findMatchingPkColumn(DocBuilder.java:718)
        at 
org.apache.solr.handler.dataimport.DocBuilder.collectDelta(DocBuilder.java:783)
        at 
org.apache.solr.handler.dataimport.DocBuilder.doDelta(DocBuilder.java:334)
        at 
org.apache.solr.handler.dataimport.DocBuilder.execute(DocBuilder.java:219)
        ... 3 more


Thanks
-Peri.S