After downloading the xap file the Silverlight object remains empty or does not showing. I tried refreshing the deployed site binaries and the xap but unsuccessfully.
Does anybody has some idea what is happening.
BTW. I have another SL site in the same domain and in the same application pool that starts without problem.
Firstly thanks to everyone for the advices. Problem is solved. Unfortunately, I still does not know the exact reason for the error. The problem was caused Plesk control panel of my hosting company that has changed some settings in web.config files when I asked then to switch a web service under a separate application pool. When we restore a backup copy of web.config silverlight page showed again. I'm not sure which is the exact cause of the problem, but this experience could be of help to all who find themselves in a similar situation.