testing the current alpha versions of mahapps.metro I currently resolve an error using a GlowBrush.
The error thrown is a "invalid window handle" in
MahApps.Metro\MahApps.Metro.Shared\Controls\GlowWindow.xaml.cs line 274.
At the moment I'm not able to reproduce that error in the sample apps contained in the mahapps.metro repository but with my own applications for example "TestUI" from https://github.com/evilbaschdi/EvilBaschdi.Core/tree/develop but I have no Idea were to search for the problem. with 1.5.0 everything's working fine.