VASSAL Does Not Start

If you cannot start VASSAL, follow these steps to determine the cause of (and possibly remedy) the problem.

Check whether you have Java for the right architecture

All OSes: Having 64-bit Java installed on a 32-bit system will never work. If you are using a 32-bit system, make sure you have 32-bit Java installed.

Windows only: Sometimes 32-bit Java fails to load VASSAL on 64-bit Windows systems. If you are using 32-bit Java on a 64-bit Windows, try installing 64-bit Java instead.

Check whether you have both Java 6 and Java 7 installed

Windows only: Having Java 6 and Java 7 installed simultaneously on Windows can in some cases cause neither to work properly. If you are having trouble launching VASSAL, check whether you have both Java 6 and Java 7 installed, and if so, remove one of them. You might need to reboot after doing so.

Check whether Java works

Open a terminal.

Windows: Open a terminal by bringing up the Start menu, selecting Run, and typing cmd into the text field.
MacOS X: Go to the Applications folder in the Dock. From there, go to Utilities, and click the Terminal icon.
Linux: Type xterm in your terminal. Heh.

In your terminal, type java -version and hit enter. You should see several lines of output, one of which contains the java version number. For example, on Fedora 18 Linux with Java 7, I see this:

java version "1.7.0_09-icedtea"
OpenJDK Runtime Environment (fedora-2.3.7.0.fc18-x86_64)
OpenJDK 64-Bit Server VM (build 23.7-b01, mixed mode)

If you see something similar, continue on to check the errorLog.

If you do not see something similar, e.g., because you got an error message instead, then java is not on your PATH.

Windows: java not being on your PATH is indicative that Java is not installed correctly. Reinstalling Java is likely to be the easiest way to fix this. Reinstall Java, then repeat the above process.

Linux: Make sure the directory containing the java binary is on your PATH.

MacOS X: ...

Check whether your firewall is blocking the loopback device

The loopback device is a network interface which has your computer as both the sender and receiver. Typically, on IPv4 networks, the loopback device has address 127.0.0.1. Personal firewalls are sometimes overzealous about blocking access to the loopback device, despite that permitting access to it is completely harmless. VASSAL uses the loopback device for communication between its parts. If your firewall is blocking the loopback device, set it to permit access to it.

Check the errorLog

If you have verified that Java runs and you are still unable to start VASSAL, do the following:

Find VASSAL's errorLog.
Post a description of what you see when you try to launch VASSAL along with the contents of the errorLog in our support forum, and we will try to help you.