SAX Error – Content Is Not Allowed In Prolog

Today, i am working and came across a weird error.not sure what was is..error is as below :=

org.xml.sax.SAXParseException: Content is not allowed in prolog.
at org.apache.xerces.util.ErrorHandlerWrapper.createSAXParseException(Unknown Source)
at org.apache.xerces.util.ErrorHandlerWrapper.fatalError(Unknown Source)
at org.apache.xerces.impl.XMLErrorReporter.reportError(Unknown Source)

Solution=After spending lot of time , i found some invalid character or element in begining of xml element
Any characters before the “