1. Go under Windows Start Button (in the bottom left of the screen), All Programs, find Java on the list and then click "Configure Java." This will open the Java Control Panel.
Can't find it? Alternatively, you can enter the below in the Start Search box.
If you have Windows 32 bit enter: c:\Program Files\Java\jre8\bin\javacpl.exe
If you have Windows 64 bit enter: c:\Program Files (x86)\Java\jre8\bin\javacpl.exe
In older versions of Java, the Java Control Panel can be found under Control Panel and then find Java.
2. Go under the Security tab and then click Edit Site List.
Press Add. Enter: http://www.iapweb.org
Can't find it?
Older versions of Java do not have an Exception Site List. Instead set the security level to Medium using the slider.
3. Click Ok and Continue on the security dialog box. Now go back to the Mars Calendar page or press this link and try the download again.
These instructions have been adapted from: java.com/en/download/faq/exception_sitelist.xml