According to my records, you already have Lad Of The Manor, Mav. So you can choose another horse.

This was your previous stable:

1 . ALL BAR ONE
2 . EL SEGUNDO
3 . EREMEIN
4 . EXCITES
5 . GOLD EDITION
6 . HARADASUN
7 . HEADTURNER
8 . LAD OF THE MANOR
9 . MENTALITY
10 . MISS FINLAND
11 . MNEMOSYNE
12 . PARATROOPERS
13 . PERFECT PROMISE
14 . RACING TO WIN
15 . RAILINGS
16 . SASSBEE
17 . SERENADE ROSE
18 . VIRAGE DE FORTUNE
19 . WAHID
20 . ZIPPING