That error is not an error. It's just a message saying you must uninstall your outdated SODE.
Your mistake was probably that, a while ago, instead of uninstalling SODE, you removed its folder without passing through the uninstaller. So, the files were gone, but its old registry key is still there.
In addition to that, at a certain point, the SODE registry key changed location, from HKEY_CURRENT_USER\Software\12bPilot to HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\12bPilot so, the orphaned one that wasn't removed is likely the one under HKEY_CURRENT_USER, and GSX checks for both locations.
If you remove it manually in the registry, the installation should proceed.
