Xcode - linking error _OBJC_CLASS_$_"className" after replacing class files
In your app's target, look in "Build Phases", in the "Link Binary With Libraries" phase.
It should include libChartBoost.a.
If it doesn't, press the + button and select libChartBoost.a.
I'm pretty certain this has something to do with the linker trying to use the references of the old files?
No. You removed the old files from the project, and that included the reference in the "Link Binary With Libraries" build phase. When you added the new files to the project, you didn't add that reference back.