I always get the 404 error when I upload a zip archive, so I changed the maxRequestLenth according to http://www.sitefinity.com/sf3/troubleshooting.html#30
It's now set to max:
<!-- Sets the allowed upload file size -->
On the upload page it now says that it's a 2GB limit, but I still get the 404 error when I try to upload an archive on 143 522 kB.
Is there another setting I'm missing?
Some global setting in IIS perhaps?