VisualStateGroups Error

I am getting the following error when building my application:

The attachable property 'VisualStateGroups' was not found in type
'VisualStateManager'. This reference comes from a theme I am applying to
the application.

Although I am getting this error the application runs fine but I cannot view
any of my pages in the Designer and get this error:

Problem Loading

The document contains errors that must be fixed before the designer can be
loaded. Reload the designer after you have fixed the...

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