Upgrade stalwart-mail.exe, lost admin login

[djcastaldo]

I had stalwart v0.8.2 running on Windows in an offline environment with no internet connection.
Webadmin was working by using a local webadmin.zip that I was pointing to in the config.toml: config.resource.webadmin = "file://c:/stalwart-mail/webadmin.zip"

This was working until I tried upgrading to v0.10.5 by replacing the .exe with the latest version, and now I can no longer login to the webadmin with the admin account. I have even tried a fresh install of the new version, but with the same result. I have even replaced the webadmin.zip with the latest one online.

Error is:
On the login page, after entering admin credentials and clicking "Sign In", the error appears:
Failed to deserialize response
data did not match any variant of untagged enum Response

I would love to get this to work. I have been trying all day.