This error could be one of two things: either there is no 32-bit Java installed to the machine, or the FileMaker Script Engine (FMSE) is not functioning properly. Both scenarios should be simple enough to fix.
Due to a hard-coded path within 360Works' plugins, a 32-bit Java is required for the plugin to initialize even though FileMaker Server 13 (FMS13) is a 64-bit process. On Windows, you can install the latest version of Java in both 32-bit and 64-bit alongside one another. I recommend updating to the latest version of Java available to avoid any possible security risks. You will need to restart the database server to reload the plugins with the new environment.
If the FMSE is not functioning properly, you can manually restart it using the command line, or you can restart the FileMaker Server Service to kill and start all FMS processes. You may need to do this twice: once with the plugin uninstalled then again with the plugin installed. Also, once the plugin is enabled, do not disable it as this can cause the error to pop up again.
Please let me know if you have any questions.