Comments by Snark Boojum (Top 1 by date)

Although solutions 1&2 is better proposals for architecture, the original question was about dynamic loading of XAML with integrated in CDATA code-behind.
Regardless of missing closing tag for the CDATA section, this XAML of yours will NEVER work because of nature of CDATA section. It({x:Code} with CDATA section) require specificaition of automatically generated class at the root tag. Only msbuild can create and compile you code from CDATA into real class and only after that XAML can be loaded successfully and binded to already existing method of that class.
In you case XamlRead begin to load your XAML and when it get to {Button Click="Clicked"} tag, it tries to bind button's event "Click" to not existing on root object(in your case - Grid) method "Clicked". Therefore it throws exception that contains another inner exception about incompatibility of signature of delegate(i.e. method "Clicked" not found).
So, forget your madness or research dynamic compilation from source code.