I'm thinking that the button hasn't finished being created before TestExcute is clicking on it. The easiest thing to do is to insert a delay before clicking on the button. This will give more time for the button to exists.
aqUtils.delay(1000)
If this proves to be the case then, you can either keep the delay or use some code to trap the error and ignore it. Then loop around to until the button exists so that it can be clicked on.
I have had issues like this. I use TestComplete on a different URL to the one I use TestExecute on. The URL that TestExecute is for a slower server, so I have to have code to cope with that.
