Cannot convert from type1 to type1 in netstandard error

Question

I've been lured into creating NetStandard libraries in 2017RC. I have come across 2 bizarre errors

• Error CS1503 Argument 1: cannot convert from 'UtilityLibrary.CountryHelpers.Country.CountryCode [...UtilityLibrary\Country\Country.cs(10)]' to 'UtilityLibrary.CountryHelpers.Country.CountryCode [Common, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]'

• Error CS0433 The type 'Regex' exists in both 'System.Text.RegularExpressions, Version=4.0.10.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' and 'System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'

After doing some searching, these are the things I've tried:

• a clean of the entire solution and build
• removing each project and re-adding them, setting the references after readding them

Why am I seeing the regex error? I literally just created a few libraries in one sitting!