Are you running SH3Cmdr?
If so, did you rollback first?
If not, then open SH3Cmdr and rollback, disable 16km optional mod then re-enable 16km optional mod again.
If this still happens look here....
http://www.subsim.com/radioroom/showthread.php?t=102303
and here....
http://www.subsim.com/radioroom/showthread.php?t=102120
BTW, Welcome