Not able to upload a file programatically in Document Library

I am getting following exception while trying to add a file :

SPException: It may refer to a nonexistent file or folder, or refer to a valid file or folder that is not in the current Web.

The issue does not occur while manually uploading the file from the browser but while adding the file in a Document Library from the code using SPWeb.Files.Add the above mentioned exception occurs. Please note that the Content DB of the web application is not full.