silverlight 3.0 control causes sharepoint 2007 login prompt in IE

[Johan V.]

Environment:
Windows Server 2003 R2 SP2
MOSS 2007 SP2
SQL SERVER 2005 SP3

I am using a silverlight 3.0 control created from an expression encoder 3.0
template in the master page of a sharepoint 2007 internet site (anonymous
access is enabled). When the user accesses the site with Silverlight not
installed he/she gets
prompted to login, but as soon as silverlight is installed the problem is
fixed. This issue only exists for anonymous users; users logged in the site
have no problem.

I have tested this with ie6, ie7, and ie8 and all these browsers prompt
anonymous users for login. I have also tested this with the latest versions
from Firefox, Chrome, and Safari browsers without any issues (i.e. anonymous
users where not prompted to login).