Join Date: Aug 2011
Location: Barcelona, London, on a plane
Programs: IB+ Gold, TK E+, Hyatt Globalist, Marriott LTP, IHG Diamond
Posts: 14,182
Spanish computer systems are often crap.
A bank once had my second surname as "no tiene", which is Spanish for "doesn't have", because their computer system wouldn't accept that some people don't have 2 surnames...
The system is possibly rejecting numbers that don't follow the Spanish D.N.I. format. If you can't leave it blank, you might have more luck entering 8 random numbers and a letter. i.e. 12345678A