This is an important trick for all web developers and asp.net experts as well,one of my dear firends asked me for a problem he faced when uploading files in asp.net web application,after justify the problem and make sure that the problem not from any other thing,the problem was he was getting [Request Time Out] when he's trying to upload large file size........the solution for this problem is :
.Net Framework by default deny upload any file which exceed than 4mb for a security reason to prohibit denial of service attack.
simply put this attribute on oyur web.config :
maxRequestLenght change the max. size from 4mb to 8mb
you can change it to whatever you want to limit the max file size.
read more on below kb article :
Enjoy .Netting :)