How to interpret validation feedback?

I’m editing a property mapping to:

| rdfs:label@en = Relates an entity to the populated place in which it is located.
| rdfs:domain = owl:Thing
| rdfs:range = PopulatedPlace
| rdfs:subPropertyOf = dul:hasLocation

When I press the “Validate” button I receive the following error:

equivalent class 'foaf:Organization' of class 'Organisation' not found

^ But notice that I have not used foaf; it was also not used by the previous definition that I modified.

How to interpret this validation error?

@wouter the validation service is quite old, we are trying to renew it soon.
Otherwise @jfrey could tell you exactly what the problem here is. He is still on holiday for some days.

You can ignore this. the error will show up for all properties and classes it they are modified/validated. the reason is that the validate process checks whether used properties and classes do exist. However, for external classes like foaf the validator complains that they do not exist in the mappings wiki.