I recently started receiving this error inside of my internal NLog failures log, with Visual Studio 2013. The solution has been using NLog v2.0.0 for several years. Within the last month, our main log stopped working. To fix this I updated NLog to the newest version (v3.1.0) via Nuget. The security exception is now gone and ALL of the log messages are appearing again.
Additionally, I later found another Security exception and was able to fix it by following the instructions on this post in another thread.