changing settlement rule for Internal Order plan version

hi,

I am trying to change the settlement rule for an Internal Order in KO02 .

I go to the settlement rule and I am trying to change the settlement rule for the plan version.

I need to add a new settlement rule with a new cost center from this period 11. But the previous rule has been used in period 16 ( This information is given in the last tab for the first settlement rule in the Last used tab).So the system wont allow me to add a new rule from period 11.

SO i went to KO9E and tried to reset the plan settlement . But the system displays a message stating that resetting not possible...as no data exists.

can anyone tell me how I can if at all resolve this situtation.

Thanks so much,

srikanth.