What do you mean? In the Java webstart application the device status is still market with "red circle" instead of green (=active reservation)? Did you try the "disconnect from server/connect to server". That usually helps, if the reservation status doesn't update correctly otherwise.
On the other hand, if you have trouble starting the Java webstart app itself, here are the first thigns to check:
* Make sure that you have Java webstart installed and that your browser can associate JNLP-files with it. Usually comes with JRE (a fairly recent version is needed!)
* Make sure that firewalls etc. are not blocking traffic to ports 80 and 1200. Port 1200 may be blocklisted by default on some setups.