New Tax Number Category creation

Hi gurus,

I am currenty finding this problem: if i go in the

Path: SPRO-> Cross Application Component -> SAP Business Partner -> Business Partner -> Basic Settings -> Tax Numbers

i am not able to create a new tax number categories, even if i have a create new button available.

if i try the message: Code your have entered does not exist in TFKTAXNUMTYPE .

and if i go in sm30 to modify the TFKTAXNUMTYPE i am not able to maintain it.

it is possible or not to create a new tax numebr category?

regards,

Gabriella