Please, note that deleting the DPSO and FODPSO is irrelevant. As long as you choose 'pso' as method it won't influence at all.
The example given in the header should work on any image:
Iout = segmentation(I,4,'pso')
If you're having a problem working with a specific image just send it to me to email@example.com and I'll try to check what's going on.