Description
You can only match using numeric attributes that exist in both the Input Features To Match layer and the Candidate Features layer. You will most often see this message when you've selected the Input Features To Match layer and the Candidate Features layer that exist in the Input Features To Match layer but don't exist in the Candidate Features layer.
Solution
The fields you select must have the same name and be of the same type in both the Input Features To Match layer and the Candidate Features layer. If the Attributes of Interest you select do exist in the Candidate Features but have a different data type or different name, you can use Add Field and Calculate Field to create new fields that match those in the Input Features To Match layer.