Why do I get a Page Not Found when trying to upgrade my account?

I keep receiving a Page Not Found when attempting to upgrade my account. In the middle of the page there is a box with the text: "Click here to retry" and "Return to the homepage." This has been going on for months and I am extremely frustrated. I've followed all of Paypal's instructions to make sure my browser security settings are correct, to no avail. I've even been on the phone with support multiple times. Someone please help! I just want to upgrade my account to the Business level.