If you see a message saying "Application Blocked by Security Settings", you need to configure the Java plugin to allow running applets on the greenfoot.org website. To do this: •Run the Java Control Panel. Read the instructions on how to find it in Windows or Mac OS X . On other systems you need to run the "ControlPanel" program in the "bin" directory of the JDK or JRE. •Go to the "Security" tab. •Under the "Exception Site List" heading, click the "Edit Site List..." button. •Click "Add"; a dialog appears. Enter http://www.greenfoot.org/, and click "Ok". •A warning appears saying that "Including an HTTP Location on the Exception Site List is considered a security risk." Click continue. •Click "Ok" to close the Java Control Panel. •You may now need to restart your web browser.

Which browser are you using? Maybe this thread could help you.

I do not get the message saying "Application Blocked by Security Settings". I get the message "Your browser is ignoring the <APPLET> tag." I have read through 5-6 threads about this, including the one where you, mkramer were having this problem. If Chrome doesn't support Java applets, and Mozilla x64 doesn't support them, will any browser work? That is, did you find explorer or edge to work, mkramer? I have added all the appropriate exceptions in the security tab for the java control center, and have made sure that Java is enabled for the browser.

My mistake (but by me that's one of the reasons it says "Your browser...", the other reason is that I have to use IE).