I've answered this question some hour ago but I see it's still unanswered, so something went wrong.
I think you are bumping against a race condition i.e. you read a value of a control or indicator and change it inside the same loop, LV does not accept it.
If your cluster is an indicator you can create its local variable, change it to read mode, unboundle, change the values of the indicators you want, boundle them back and in the next loop you can set the new value of the cluster (you should use a shift register).
You can use an alternative method that lets you change the values you want of the indicators in your cluster in the same loop. It is based on the property nodes of the cluster, see sample vi attached.For a description of the property node used open the help
window.
Hope it helped.
altek@tin.it