Hello James Harkins,
You have to manually remove the assemblies from the GAC, in order to "clean-up" manually from the previous installation (I don't have a clue what went wrong, but you are right, it looks like parts of the previous version are still there).
You can uninstall Telerik OpenAccess ORM, and after that open the Windows File Explorer. If you navigate to the C:\Windows folder you will see a folder named "assembly". Opening the folder provides you with a view of the 2.0 GAC - just search for assemblies names that have Telerik.OpenAccess.X, Telerik.Data.X or Telerik.VS.Data.Design and delete them. The same applies to the 4.0 GAC which can be found under the C:\Windows\Microsoft.NET\assembly\GAC_MSIL folder - please repeat the same action. After than making a clean OpenAccess install will solve the issue you have now is my expectation.
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