loadrunner Vugen file upload replay error

Hi,

I have recorded web script using HTTP/HTML protocol. The business process includes uploading multiple documents. There was no issue recording the script. I have placed the document/files in the script folder. 

However during replay, it gives errror "Warning -26490: File name in a multipart submit is missing or empty. Using an empty file".

Any advise or inputs will be appreciated.

Thanks