Error Message: Varies. "Page Cannot be Displayed" is common

Description:
When a user uploads a large file or has a slow connection, the file upload fails with various error messages 

Reslolution:
Connection timeout and file upload size between the client and the server is controlled in the Web.config of the DNN installation. Depending on your Host you may not be able to override these settings.

File Size is controlled by the maxRequestLength attribute in the httpRuntime Element. The ASP.NET default for this is 4096 (4meg). When a file exceeds this size the user will get an error, possibly "This page cannot be displayed". In this case since the request has not been handed off the Web Application yet, Form Master is not even involved.

Timeout is controlled by the executionTimeout attribute in seconds. The default is 45. The httpRuntime modifications shown below is actually from the documentation for Speerio's File Manager Pro, and is recommended by Nik Kalyani. Nik is a DNN Core Team member and produces great modules.

See if the modifications below help your situation.

The settings below allow 100 meg file size and 20 minutes timeout.

[httpruntime executiontimeout="1200" maxrequestlength="10240" usefullyqualifiedredirecturl="true" /]

All about the httpRuntime Section: