c# - NotSupportedException thrown when instantiating a DataContext on wp8 -

i'm using vs2012 express, writing in c#, , targeting wp8. testing being done emulator.

i've been following example here:
http://msdn.microsoft.com/en-us/library/windowsphone/develop/hh202860(v=vs.105).aspx#bkmk_usingthedatabase

my problem is, every time try instantiate datacontext object (well, derived class) notsupportedexception in system.data.linq.ni.dll. line throwing exception constructor calling base(connectionstring).

any idea i'm doing wrong, or how can more information me sort out?

apparently db files can use sdf extensions. when modified name of data file use .sdf, worked fine.