If you have any Silverlight Web Resources in your site map that are hosted by an HTML Web Resource, you may find that when you upgrade to CRM2013 and use the pull down Application Bar the Silverlight page is rendered on top of the navigation buttons so that they are obscured and hidden from the user.
It might look something like the following:-
To fix this you need to adjust the Windowless…
Continue Reading Develop1’s Article on their blog
How to fix CRM2013 Application Bar hidden by Silverlight Web Resource
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