Window Staining

Anybody have an Idea what would be causing this? appears to be a tar/sealant that has leached out during hot weather.

House was built in 2005/2006 Andersen clad windows.

Please read through the below link, it may help you.

http://www.inspectionnews.net/home_inspection/building-envelope-home-inspection-commercial-inspection/27063-melting-window-flashing.html

Thank you William,
That forum link did help, I was thinking that was the possible cause.