The existing M_TAXI is not usable by the query that threw the exception. Please try inserting
<datastore-index kind="M_TAXI" ancestor="false" source="manual">
<property name="cityName" direction="asc"/>
<property name="updatedOn" direction="asc"/>
</datastore-index>
into datastore.indexes.xml before the </datastore-indexes> end tag and after the other M_TAXI element, and report back what the result was.