That path is not where I would expect to find it.

Try following the instructions here:

https://www.att.com/support/article/u-verse-high-speed-internet/KM1046931/

I received this error message as well from att.net/iss

An unexpected error has occurred.

• Check the web address you entered to make sure it is correct
• Visit the McAfee home page
• Go to McAfee Support
• Return to the Previous Page

I am assuming that you were allowed to sign in, and select the download you wanted before that appears?

After entering your suggested web address.  I pressed "got it" entered my password.  Then I selected English as the language and then the web page redirected me to the error message.  After talking to both Macafee and At&t tech support it maybe that AT&T hasn't paid Macafee for the Antivirus software? 

I really don't think that's it, because after I click the English Download button, I get (eventually) redirected here:

Hello @usdafred, we will be happy to offer some assistance with the AntiVirus software.

When it comes to trying to download it, we recommend following the AntiVirus Plus Installation Guide to ensure it is being installed properly. Before doing so, it is good to know you should uninstall existing, security software before downloading the AT&T AntiVirus Plus. Once you have done that, you can follow the steps below:

• Go to AT&T AntiVirus Plus and select Download Now.
• Enter your AT&T user ID and password.
• Choose your option. If you have internet speeds of:
  
  • 3Mbps or higher, go to Step 4.
  • 1.5Mbps or lower, select Buy Subscription. You can purchase a subscription for $5 per month.
• Follow the prompts to download and install AntiVirus Plus.

It is important to know that you'll only e eligible to get the software on the account that's linked to the correct service.

Please let us know if this helps.

Lani, AT&T Community Specialist