IIS File upload fails for large files returns 404

This could be because the request filtering in more than the allowed size limit.

Check the iis log files to get a request code. It would be something like,

links below has more info on the substatus message:

http://www.iis.net/configreference/system.webserver/security/requestfiltering/requestlimits

http://www.zquad.in/2010/07/iis-error-log-code-sc-status-and-sc.html

Solution: if 404.13 is the status then increase the allowed content size then go to Request Filtering option in the IIS under the particular site and select Rules->Edit Feature Settings on the right hand pane and increase the value for Max allowed content length.