Cannot upload files larger than 30MB to Amazon

Question

Our site is hosted in Amazon EC2 server and files are stored in Amazon S3 server.

My problem is when I upload files larger than 30MB, uploading failed. Does not display any error, but connection reset. the page display like this

The connection was reset
The connection to the server was reset while the page was loading.
The site could be temporarily unavailable or too busy. Try again in a few moments.
If you are unable to load any pages, check your computer's network connection.
If your computer or network is protected by a firewall or proxy, make sure that Firefox is permitted to access the Web.

But if I upload smaller than 30 MB there is no issue or error. Please help me in this issue.

In my config file we are using

<httpRuntime executionTimeout="120000" maxRequestLength="1048576"
             useFullyQualifiedRedirectUrl="false"/>

so that, it should allow around 1GB file.

We are using single part uploading, in Amazon document says that single part uploading also allow 1byte to 5 Gb, then what is the issue?

Please help me soon