This web site keeps track of your current username and password in a small file called a cookie. This cookie allows you to navigate around the site and use the various features without having to log in constantly.
You may be using firewall software such as ZoneAlarm to protect your computer. By default, ZoneAlarm prevents the use of site cookies.
To resolve this problem, configure ZoneAlarm or any other firewall software you are using so that niebuhrgathering.com is a trusted domain.
In ZoneAlarm, you can do this by clicking the Click here for details link in the popup that appears when you navigate your browser to the site. In the list of web sites that appears, find niebuhrgathering.com and make sure all the columns to the right of the site name contain checkmarks, not X's. Click each X and select Allow.
Another possibility is that your web browser - or a security add-on for your browser - is preventing cookies from being used. Again, you can resolve this by disabling that feature completely (most cookies are harmless), or configuring your browser or security add-on to allow cookies from niebuhrgathering.com.