If your Act! for Web login page shows up, lets you login and then shows up again there are a few steps which might resolve this issue.
1. Allow Pop-Ups
Pop-Ups allow your browser to communicate with you without switching the website or reloading it which is a good thing for little notifications and requests like „Are you sure you want to delete this contact“ or „The contact you´re trying to create is a duplicate. Would you like to proceed ?“.
Those two examples are built into the workflow when working with Act! but on the login there might be Pop-Ups as well requesting you to change your password or telling you that you have tried to authenticate with the wrong password too many times and have to wait now. If you don´t allow the Act for Web site to show you such Pop-Ups then the login won´t work as expected
2. Clear your cache or load the website without it
The browser cache stores some data to make the web experience faster and better. Unfortunately this also sometimes causes unexpected situations.
If anything doesn´t work as expected with APFW simply try to reload the page using CTRL + F5 simultaniously which will lead to a reload of the page ignoring data that is stored on you´r browser so I will be fetched from the Website.
3. Clear your cookies
Cookies are a great thing for websites since they allow to store data in your browser with very little effort. It´s often used to save things like the position of a slider, the last contact you opened or your session id. If any of those is faulty then the Act! server might get confused and simply refuse the login or similar.
Simply try to clear your cookies and try again. In Google Chrome this can be done by navigating to the browser settings, in the left menu navigate to „advanced“ -> „safety“ and choose „Clear browser data“ An Pop-Up will open where you can select „cookies“ and then click „Clear data“.