When utilizing a geoprocessing tool and specifying layers with identical names but differing sources as inputs or targets for the tool, a red X with the following error message is returned:
"Duplicate inputs are not allowed".
The geoprocessing tool validates layer inputs exclusively by their layer names. The tool treats both inputs as coming from the same source, and will not execute until one of the conflicting inputs has been removed.
One of the layers with the same name needs to be modified for the geoprocessing tool to accept both layers. The layer name can be modified by selecting one of the following methods: