We had an ACT v19.2 client unable to use the remote internet login via ACT Premium Web access. When they got to the sign-in screen for ACT it showed the database name correctly, but the username and password prompts were greyed out. You weren't able to type anything in those fields and consequently were unable to login.
At first we suspected some Microsoft updates to .NET that had been loaded on the server over the weekend. However it turned out to be less obvious, the Protexis Licensing V2 service that is located on the ACT server had stopped and failed to restart. Once this was started again, the ability to type username and password in the browser was restored.