If a student uses a comma (,) in their answer for a Numeric question in a Quizmaker '09 quiz, the question may be marked as Incorrect.
This is a known issue. To avoid this issue, you could use a Fill in the Blank question type and specify possible answers with and without commas.
Another workaround for this issue is to instruct your students to refrain from using commas in their answers. You might consider adding a text box with simple instructions to avoid using commas (in Slide View) as shown in the image below.