hi.
This message is telling you that there is something wrong with the movement file. You will need to check your road movement files (rds) for the locations Sand_Beach to Sand_Island. It could be that the distance between the two points may not be set far enough a part and they are be too close or the route may not be possible due to game limitations, such as a land vehicles crossing water or being to close to the waters edge to get to an island. It may also be a name mismatch like a sea designation location being used for a land movenment location or that the map has an error such as a bridge missing making it impossible to get to the end location Sand Island.