Two-Factor Auth v4.6 - older
This is no longer supported. A clean installation will need to be performed.
Two-Factor Auth v5.0 - newer
If you are using 2FA v5.0 please see this article: Two-Factor Auth upgrade guide from v5.0 to v5.6
Note: With the release of 2FA v5.5 x86 servers are no longer supported. You will need to be using an x64 server as per https://helpdesk.kaseya.com/entries/25881456