It is difficult to say what may be causing the problem for you without a little more info about the setup and what steps you are taking.
How did you implement the multiple insert? Please review the steps that you have taken to get this into place. If something in the process is not done correctly or is out of order issues can arise so please explain with as much detail as possible the steps you took.
What is the version of DataAssist that you are using for this? This will help if I need to do any testing to check on the result you are getting. This information can be found in the extension manager or by going into the Help > WebAssist > DataAssist > About. At the time of this post the most recent release is 2.0.6.