In IIS7 environment, there are several limit for ASP.NET can be override by web.config. One of error could be follow:
The request filtering module is configured to deny a request that exceeds the request content length
This problem occurs because by default in IIS 7 enabled requestFiltering that have MaxAllowedContentLength property. It specifies, in bytes, the maximum length of content in a request. The default is 30000000 (approximately 30 megabytes.)
To override the default setting, you could add following to web.config:
Notice above situation only occur on IIS7 or Windows 2008
Regarding asp.net upload size limit, there are other limits like executionTimeout & maxRequestLength. If file upload larger then the limit, "Maximum request length exceeded. " error will be shown.
You can add to the site web.config like follow:
Please note that with higher executionTimeout value your site will be more vulnerable by DOS attack.