Setting IsCollection on TypeDescriptor with Name '{0}' and Id '{1}' (belonging to Parameter with Name '{2}' and Id '{3}') ...

Setting IsCollection on TypeDescriptor with Name '{0}' and Id '{1}' (belonging to Parameter with Name '{2}' and Id '{3}') will create a collection TypeDescriptor with more than a single child. Collection TypeDescriptors may only have a single child TypeDescriptor, representing the structure of each element of the collection.