I assume this is the default Java System Http Availability metric that comes from the templates of a 7.3x/7.4 system and the metric is looking for the /startPage value, can you reach that on your browser?
If this BW Java system is still on 7.1x or 7.0x the metrics look for a /index.html.
Depending on your requirements you could edit the default metric and change the URL to something that does respond so you know the stack is responsive.