Error when closing a process order

Hi

I am getting an error when trying to close a process order.

The error is - KW407"No prices could be determined for object Activity type XXXX/XXXX/SET". I have checke the following:

1. KP26 the price has been maintained.

2. Have checked that the cost element assigned for the actuvuty is "43"

3. The Valuation variant is maintained correctly.

Please let me know what could be wrong and how the order can be closed.

Karthik