dbFront stores an encrypted key in the users session. The "Session Key Failure" error means that this session key has been lost or corrupted.
Because this error is happening consistently, the most likely reason is that the browser is loosing the session cookie forcing the server to create a new session everytime.
One recommendation when securing servers is to add the setting [httpCookies requireSSL="true"] to the web.config. This ensures that cookies are always sent and received using SSL. For more details see: Penetration Testing Issues
If this setting is enabled on the web server then any requests using HTTP potentially have their session cookies dropped. This is known to happen with IE 11 (Internet Explorer).
The URL http://localhost/dbFront, does not use SSL and so some browsers like IE can't retain the session.
If you consistently need to access the local environment using the URL http://localhost/dbFront then the simplest option is to install a current browser such as Brave, Firefox or Chrome.
Another option is to simply use the URL https://localhost/dbFront. This URL will cause a server certificate error but you can easily ignore this error and proceed to use dbFront.