If you have this exception “Xaml Internal Error error WMC9999: Access denied” while compiling a WinRT or UWP project with Visual Studio, the solution is :
- Close Visual Studio
- Delete or rename the “packages” nuget cache directory of the project
- Restart Visual Studio
You can check with “process monitor” on msbuild.exe to know which DLL have an Access Denied (in my case, it was BCL task library but I guess it could be anything else) if it’s not Nuget, maybe an other referenced DLL have an access denied !