Controlling two machine in on VI

Hello everyone,

I have two instruments. One is autowave and another VDS. I need to controll them from same vi. Is it possible?

Here is what i want to do:

1) at first set initilize autowave

2) initilize VDS

3)Send wave form from Autowave.

I put these three cases in a state machine. They work as expected. But problem it is stuck in the third case. AS a result, I get the error below. "Object reference is not valid". I think my state machine doesn't reach to the third state. It could be because i am using the same instrument in State on and three.

I don't how to use Autowave then VDS and then go back to autowave to do the 3rd task.  

Thanks in advance for any clues.