I have this happen EVERY time I do a DNN4+. I have to change the machine.config file to remove the line thats now somehow gotten into that file when I was testing a build. I did report it, and was told something was changed so this shouldn't happen again, however, for me it does, as well as lots of other little quirks about DNN I rarely bother to report any more. I found a work around.
Since it even affected a NON DNN installation I did on the xigla software, it made me aware that it had in fact affected my machine.config file which I am not really comfortable in changing.
However, to get around it - this is what I do - Unzip the package you are installing, the put the folder in, and then zip it back up again. If you are setting up sites manually, like I am for now - then you will need to make sure it's in there before hitting the build button.
Since I strip back the DNN installation file anyway, it' not a problem any more. I don't install that module anway - so I find it doubly frustrating because you'd think if it wasn't there it shouldn't happen.
If it continues to happen, then I would say you need the machine.config file in the windows aspnet framework folder.
So try that and see if doesn't make a difference to the installation.
Nina Meiers