To start with, I would like to stress that I do know how to define XML Namespaces correctly in my XAML files. This repeated error is not caused by an mistake in my code. The problem does not stop my project from being built successfully, or running and the mentioned Converter class works perfectly.
When I build the project, the errors disappear. However, the designer show the familiar error message:
When I click on the 'Reload the designer' link, the errors return. The worst part of this problem is that I lose all Intellisense on these views.
The error highlights these namespaces:
But you can clearly see that they have been declared correctly:
I'm sure that I have found a solution for this problem before, but after an extensive search just now, I can only find a million posts relating to this error where users have actually made errors. Please also note that this was a brand new WPF Application and not downloaded from the internet or a network drive.
Is the project ON a network drive? XAML has issues with projects stored on a network drive. In corporate environments your Documents are often remapped to a network path, causing this problem for the default project folder.
Try like c:\projects\yourprojecthere instead?
来源：https://stackoverflow.com/questions/18659708/why-do-i-keep-getting-assembly-must-be-specified-for-xaml-files-that-are-not-pa