Hi Rahul,
There are basically two places where account determination settings are maintained.
(1) For revenue account determination
(2) For reconciliation account determination.
Since you mentioned that the account assignment key is not determined for the condition type KOFK, I assume that you are facing the issue with the reconciliation account determination.
I have faced this issue in the past and more times than not, the condition table being used for account determination (assign G/L account) is not the correct one that is assigned in the access sequence. I hence suggest that you check the whole condition technique thoroughly, starting right from the procedure assigned to the billing type, the condition type assigned to the procedure, the access sequence, right through the condition table/tables maintained.
This should hopefully solve your issue. It did in my case 
Regards,
Sumita Mittra