Hi Mimi,
We need more information. There isn't enough information in your query to make any sort of useful response. It would help if you could start out by giving us some general information about the experiment.
1. What kind of dataset are you looking at?
2. What was the syntax of the command you used?
3. What were the expected results?
4. What results did you get?
5. How did your results differ from your expectations?
One reason clusters don't show up is that they may look like they are contiguous from one slice to the next, but upon close examination, they don't actually share adjacent sides.
-jim
