IIS 7.5 does not respond to request object

<div class="content btf-content"> <div class="first last">We have an old vb6 application that ran perfectly on IIS5 with no issues. The user was able to submit large amounts of data and the application would post back with no issues.
We have now moved to IIS 7.5 and there appears to be an issue. If the user post submits more than 369,809 bytes of data the application will not respond.
 We have bumped up the maxAllowedContentLength up to ="4096000000" in the webconfig file but it still will not post back.
We have run the Request Fail tracker but it does not report any errors. The result status is 200.
We ran fiddler2 and same results status 200. The Response Content length is coming back as 0.
The application run great on our local machine which is an XP virtual machine that has iis 5 installed on it. We are able to save large amounts of data to the web site with no issue.
When we try running the application on the server on iis7.5 it bombs.
It appears that it does not evalute the the request form object on the server side. It simply skips over and exits the page with reporting an error</div> <div class="first last">it bombs at Response Headers Entity Content-lenght :369809</div> </div>