That happened to me in beta testing. My first version (before I bailed) was named...
Blablabla. After getting the same message that you did, I re-named my mission...
blablabla1. then it accepted the mission.
Since submitting a final mission (may) not be the same as beta testing, you might want to mail the "Mission-depot-dudes" and tell them (or wait for ADMIN or someone not as trashed as me) to tell you that everything is .... :toocool:
James, I wanna go home now