by default asp.net application did not upload file more than 4.5 mb or 4 mb. For this purpose You have to add following http runtime tag in web.cofig of web site.
<httpRuntime executionTimeout=“90“ maxRequestLength=“20096“useFullyQualifiedRedirectUrl=“false“ minFreeThreads=“8“ minLocalRequestFreeThreads=“4“appRequestQueueLimit=“10000“;/>
you have to change two setting in above code.MaxRequestLength (Here you mention the size limit of file , bydefault it is 4 mb) and appRequestQueueLimit (it is the time when application take time to upload the request.)