Why it is asking to update Silverlight version

So  many times I have seen this type of messages in dev environment.Now understood what was the reason..I was doing the same without knowing the actual facts.

http://timheuer.com/blog/archive/2010/09/28/keeping-your-silverlight-dev-environment-stable-through-service-releases.aspx

Getting Silverlight version

Here is the post which gives you how to get the Silverlight version through Javascript.
http://www.kunal-chowdhury.com/2010/09/how-to-detect-installed-silverlight.html

If you want to get the Silverlight version inside Silverlight code you may invoke this function as follows.
http://silverlightedweb.blogspot.com/2008/05/silverlight-javascript-communication.html