See if you can create a character using the 'default' uniform selection (Don't change the uniform) as some of the uniform options have been known to do this in the past... (You can always change your looks at the tailor when you make it to ESD..)
I tried again without changing uniform but still failed to create.
So I deleted the dummy character in the 'Create Content' area and then tried again with the normal character and it worked. I was only playing with the content creator just for curiosity, so not really that important.
The odd thing is I had 5 free slots before I created the dummy one - which it says will use a slot. However, I still had 5 slots after creating that. Perhaps that is relevant?
Now I have successfully created my Bajoran Tactical Officer I have 4 slots free - which makes more sense.