Back in August I wrote a post about how to debug these types of issues in silverlight applications. 

Since Silverlight 2.0 RTM’d this is now a bit more relevant so just wanted to refresh your memory that you can debug these types of applications and issues with windbg and sos if neccessary.

http://blogs.msdn.com/tess/archive/2008/08/21/debugging-silverlight-applications-with-windbg-and-sos-dll.aspx

The version numbers are different now but all the rest is the same.

Tess