I mean you need to run your program under the debugger to trap exactly where the error occurs, what the error is, and what variables, pointers etc. are possibly causing the fault. Without that information it is impossible to guess what may be going wrong.
As a warmup for a more complex project in C#, I have started to code a C++/CLI library to allow simple access of C# applications to features of DirectWrite. (I am aware that there are such helper libraries already out there but I was not able yet to get them to work with in Visual Studio 2015 and with Windows 10.)
So far so good. A first test run showed the text in the target window but not as I would have expected for ClearType display. A screenshot of the displayed text can be found here.
My understanding of the relating MSDN documentation is that ClearType is enabled by default. The title bar text of the window is obviously set up with text in ClearType. I guess I missed a setting in the DWrite factory but I do not know which.