Hi Boatsarefun,
As Tore said, both pickup and drop must be set to either zero or a positive integer. Leaving either at -1 will not work.
If you have not already done so, you can download the Mission Editor Tutorial from here:
http://80.95.161.114/shipsim/forum/index.php/topic,2886.msg28895.html#msg28895 (http://80.95.161.114/shipsim/forum/index.php/topic,2886.msg28895.html#msg28895)
Under TAXI WAYPOINT: 7. It explains the need to specify both numbers.
You can always ask me any questions about the editor either by PM or email to the address in my profile.
Regards,
Marty