I backed up all my files, copied in all my new files, then started my DNN site.

I set it to auto upgrade and went to http://www.mysite.com/install/install.aspx?mode=install and got a 404.

What causes this and how do I fix it??

Meanwhile I turned off auto-upgrade and tried again with manually navigating to the upgrade page and this did not work, either.

I do have a site backup to which I can return and try again...

How do I get the upgrade to work properly?? The install files ARE there, so I don't understand why I am getting a 404.

I've also tried a couple times rebooting the server, it's a test/dev server.

Thank you, Tom

Yes, I have backups.

I unzipped the 4.9.1 file, then copied everything into wwwroot, where my site is located.

I have done it this way before.

Yes, the /install/install.aspx file is in place and I can see the updated directories, module and package.

I also checked all the permissions, I'll try one more time with the unzipping...

Thank you, Tom

that's very strange, there seem to be something interfering. you might try to add a simple index.aspx and try to call it to validate, that ASP.Net is running fine.