Quote:
nothing seems to work
... and it never will.
First, it only ever works on your DEV machine because everything, including the web server, is running as YOU on your desktop.
When deployed on the server, everything runs as a service without any visible desktop. So, the dialog that shows up only shows up on the web server where nobody can see it. The dialog will NEVER show up on the client machine.
Also, Excel Interop (what you're doing) can NOT be used in a web application for various reasons, like re-entrancy and multiple thread problems. It may work so long as one user at a time is using a function in the website but it will fall on its face and crash with the more users using the functions at the same time.