[Solved] Unity IAP Installer Fails

I get this error when I try to use Unity IAP Installer. Using Unity Version 5.6.3f1. Was getting the same error for the most current build, I downgraded to 5.6.3f1 to see if it would work; it didn't.

Code (CSharp):

1. ReflectionTypeLoadException: The classes in the module cannot be loaded.
2. System.Reflection.Assembly.GetTypes () (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/Assembly.cs:371)
3. UnityEditor.Purchasing.UnityIAPInstaller.<GetPurchasing>m__0 (System.Reflection.Assembly assembly) (at Assets/Plugins/UnityPurchasing/Editor/UnityIAPInstaller.cs:101)
4. System.Linq.Enumerable+<CreateSelectManyIterator>c__Iterator14`3[System.Reflection.Assembly,System.Type,<>__AnonType0`2[System.Reflection.Assembly,System.Type]].MoveNext ()
5. System.Linq.Enumerable+<CreateWhereIterator>c__Iterator1D`1[<>__AnonType0`2[System.Reflection.Assembly,System.Type]].MoveNext ()
6. System.Linq.Enumerable+<CreateSelectIterator>c__Iterator10`2[<>__AnonType0`2[System.Reflection.Assembly,System.Type],System.Type].MoveNext ()
7. System.Linq.Enumerable.FirstOrDefault[Type] (IEnumerable`1 source)
8. UnityEditor.Purchasing.UnityIAPInstaller.GetPurchasing () (at Assets/Plugins/UnityPurchasing/Editor/UnityIAPInstaller.cs:103)
9. UnityEditor.Purchasing.UnityIAPInstaller.EnablePurchasingService () (at Assets/Plugins/UnityPurchasing/Editor/UnityIAPInstaller.cs:459)
10. UnityEditor.Purchasing.UnityIAPInstaller.Install () (at Assets/Plugins/UnityPurchasing/Editor/UnityIAPInstaller.cs:314)
11.