HI ,
This happens when you have a previous version of the Datasmith plugin that does not uninstall correctly, and you try to install another version of the plugin. Please try downloading the previous version of the plugin (version 4.27v2) from https://unrealstudio.epicgames.com/UnrealDatasmithRevitExporter_4_27_v2.msi
Please try installing it, then when the installation completes use the Windows uninstaller to uninstall the plugin.
Once you have uninstalled the old version, try installing the new 5.0.3 version again, which should work now.
Best,
Raghib