Content is not allowed in prolog

Dear Experts,

I have implemented a scenario using SFTP as sender and SOAP as receiver.

A txt file is getting picked from thr SFTP adapter, However in SOAP adapter logs m getting the below exception.

MP: exception caught with cause com.sap.engine.interfaces.messaging.api.exception.MessagingException: java.io.IOException: Parsing Error: org.xml.sax.SAXParseException: Content is not allowed in prolog.

I have implemented this scenario using ICO and its a passthrough scenario, so mapping handling is there on runtime.

Please advise to get rid of this issue, if someone has also got the same.

Thanks

Zeeshan