Reference required to assembly '|1' containing type '|2', but a suitable reference could not be found due to ambiguity between ...

Reference required to assembly '|1' containing type '|2', but a suitable reference could not be found due to ambiguity between '|3', which is referenced by project '|4', and '|5', which is referenced by project '|6'. If both assemblies are identical, try replacing these references so both references are from the same location.