See this thread. http://forums.ni.com/ni/board/message?board.id=200&message.id=5197
It states that there is a bug in Vision Assistant 7.1. that is fixed in Vision Assitant 7.1.1.
If you are using VA 7.1, you will need to get an upgrade to 7.1.1, although I couldn't find it anywhere in the "update and patches" download page. I'm using VA 7.1 also, and am having the same problem. I emailed my local NI rep last week, but haven't heard a word from him. You know what they say about "service after the sale"!
I hope this helps you.
Dan Thomas