There are many possible reasons why this might happen. Could you give us a bit more information about your scenario settings? Perhaps list the datasheets that are specified for your scenario. In version 2.2 this is under the final tab in the scenario properties. In version 2.3 it is in the final node of the General tab (first tab). You should check that you have non-zero probabilities for your transitions and that the states where pathways are defined are actually occurring on your landscape.