Sometimes troubleshooting DNN errors can be a royal pain. Fortunately, if you know what you're looking for installation errors are usually pretty easy to resolve. Unfortunately, if you don't know what you're looking for or if you're a DNN Noob, you may be bald by morning.
If you've just installed DNN and receive this error as soon as you attempt to open the site in your browser, you may not have a web.config file defined.
Depending on which DNN package you selected to download, you may or may not actually have the file named, "web.config" in your root directory. DNN Starter Packages come with three config files:
- Web.config
- Development.config
- Release.config
You don't need all of the files however, the only one you actually need is the web.config file. The other two allow you to set up different config settings for testing or what not.
Now, if you've downloaded the DNN Source Package or Upgrade Package, you are not going to find a "web.config" file. The reason for this is so that you don't accidentally or inadvertantly screw up what you've already got going on. If you download the upgrade package and upload your files over your existing files, guess what? All those customizations you've done to your web.config file are gone and you're a mad mofo! Similarly, the source package includes the Development.config and Release.config files so you can make your adjustments as you're going along.
As a result, what happens sometimes is that people download the DNN Package ("there was more than one kind???") and immediately begin to try to run it. If you're using the default setup, typically you can do this…so long as the server can find your web.config file.
Check out the project directory in the image below and you can see what I'm talking about. Luckily, it's a super simple solution…simply rename either Development.config or Release.config to "web.config". Or, if it gives you the warm fuzzies to keep all the files you downloaded in tact, just make a copy of one of thm and then rename it.

Here you can see that I simply chose to rename the Release.config to web.config

Now, navigate to your site and Voila! Welcome to either a shiny new DNN installation or the next error to fix! J Either way, you're over this one now.
