Quick question, does your activity level when using oDesk team affect how much you are paid or is it there for reference only? I only ask because I primarily use oDesk for programming work, and in that line of work there are often times when I'm not typing away but rather thinking.
The activity level doesn't affect how much you are paid, the client will still be billed for the logged time. However, time logged with low activity will not qualify for oDesk Guarantee in case of a dispute or issues with the client's payment method. As Marcia suggested, you should communicate with your client and let them know why activity levels are low or ask them to allow manual time.
Please, let us know if you have any further questions.