Issues/Symptoms:
You have uninstalled Revit 2014 / 2015 and need to reinstall. When you attempt to reinstall Revit 2014 / 2015, the installer reports itself as already being installed, which you know is not true, since you just uninstalled Revit 2014 / 2015. You're unable to install Revit 2014 / 2015 again.
Resolution:
For a clean Revit 2014 / 2015 installation, verify that Revit related registry keys listed below are removed from the system after Revit is uninstalled. Typically Windows Installer clears these keys, but not in this case.
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