change the validity date in change number

hi team,

I want to change the validity date of a change number from 01.01.09 to 01.03.09. I am getting an error "A BOM has already been changed using a change number with the same valid-from date as the selected date 03.01.2009". I can change the date to before 01.01.09 but cannot after 01.01.09.

Can you please help me.

thank you,

Satish