So the problem is when i try to setup breakpoint on line with Binding markup extension I get error telling me that it’s unable to set breakpoint in this location.
Visual Studio
Microsoft Visual Studio Ultimate 2012
Version 11.0.50727.1 RTMREL
Microsoft .NET Framework
Version 4.5.50709
Installed Version: Ultimate
Platform settings

Platform targets are x86 for all except Silverlight ( selection box locked there)
Debug info is set to full everywhere.
Debug settings

Cleaned up and rebuild solution with no errors.
Go to line with Binding press F9 or Debug->Toggle breakpoint and see:

When I had this I error I could usually solve it by doing the following things:
Make sure that Silverlight debugging is enabled:
Project properties -> Web -> Debuggers -> Activate theSilverlightCheckBox.Use the Internet Explorer for debugging. Although it may work with other browsers, I often ran into strange problems like the Breakpoints not being correctly set.
Most important:
Clear the IE browser cache. It is most likely possible that the browser has cached an older version of your Silverlight application and for some reason does not use the latest version of it.
If this works for you, you miht also consider to configure the caching of the temporary internet files to “Never” to make sure that IE always uses the most recent version of your SL application.