Problems accessing archived items

First thing first, if its urgent, open a case.
Secondly if you're on EV8 and you checked the box on the site properties to use HTTPS, then you have to synchronize the users (and have them restart outlook) and run restoreshortcutbody to fix the URL links with in the messages themselves.

403 forbidden tends to be when the IIS website is using a white list to allow only specific IP addresses to connect to it.
You also may have gotten the /EnterpriseVault virtual directory set up or the default website even to only allow https communication

so you can do one of the following

1. Check in the IIS properties of the default website that you haven't set it to require HTTPS or removed HTTP port
    - right click the default website, go to the properties and on the website page, make sure TCP Port 80 is in the TCP Port

2. Check the IP Address allow list
    - In IIS right click Default Website, go to Properties and then go to the Directory Security tab, then click the middle "Edit" button under IP Address or domain name restrictions. Ensure that Granted Access is checked with the exception list being blank

3. If all else fails, go to IIS, right click "EnterpriseVault" virtual directory, click delete and remove the virtual directory
    After this go to Start -> run -> type "cmd" and press Enter, then type "cd \Program Files\Enterprise Vault" and press Enter , then type "cscript WebApp.vbs" and press Enter, then after this try again