mb11 and mb1a 261

dear all

plz go thru blow problem and plz help me to resolve...

scinario:-- i am selecting mb1a or mb11 by selecting plant ,mvt , and go to orders i am getting new screen where i mention PM breakdown maint order and i select adopt details, then a new screen appear with all details of PM order, like material code, qty, batch ..excepttttttttttttttt Costcenter...

and this field also showing GREY, so i cannt able to put costcenter manuaaly as well...

can anyone suggest me how to resobe this?? how can i get cost center by defalut which i maintain in PM order (IW31 tcode)??

or how can i make costcenter field as modifiable and Mandatory field??

Plz help