Mumsnet local site- problems with nicknames?

[Ribeno]

Hi all, I have tried to start a thread on my local mumsnet site but every time I choose a nickname, a message flashes in red saying choose another nickname. Anyone know what im doing wrong?
Thanks

[AnyaKnowIt]

Might be worth asking in site stuff?

[Arithmeticulous]

Aren't you supposed to have a different nickname for local?