hi Lalitha,
I got this working by following the steps in kmkdz's and marianol's answers.
Initially I got a "jrruntimeexception org.exolab.castor.xml.MarshalException" with the message "The processing instruction target matching "[xX][mM][lL]" is not allowed". Turned out there was a blank space at the begining of my xml document.
After that I got a "jxl.read.biff.biffexception Unable to recognize OLE stream" which got solved by converting the .xlsx(Excel 2007/2010 format) to .xls(Excel 97-2003 format).
Hope this helps!
Best