The reason behind this error is the file size exceeds the ASP.NET maximum request length restriction. By default this value is 4 megabytes, if you want to support request greater then it then u need to increase limit in web.config file.
< system.web >
< httpRuntime maxRequestLength="1048576" / >
< /system.web >
< /configuration>
this will increase your request limit to 1 GB.