I ran into an issue with a DNN site we are developing in DotNetNuke 4 and the ability to install modules from Host > Module Definitions > Add New Module. After selecting the module and clicking Upload, I was immediately redirected to the Module List page, without installing the module. The weird part was that it did not cause an issue with all of the modules I was uploading, only a few of them. Without turning debugging on, and finding the true root of the problem, I simply did the following:

1. Dropped the modules I wanted to install into the \Install\Module directory.
2. In a browser, navigate to http://www.domain.com/install/install.aspx?mode=installresources

DotNetNuke will then install the module and you are able to continue with your development. Yay!