Namespace error when building to UWP

Hello, first off this is an amazing asset.  Everything works great when I build using the windows stand alone format, but when I try to build using the UWP format I get the following error:

"Assets\Skele\Common\Xml\SmallXmlParser.cs(614,43): error CS0246: The type or namespace name 'SystemException' could not be found (are you missing a using directive or an assembly reference?)"

I am using Unity version: 2017.1.1f1 personal

Any help with this will be greatly appreciated.  Thank you.