ZBrushCentral

ZSPHERES dissapears in my canvas?

Hello:
During the method of create a body or a objet with zspheres , my zspheres dissapears in my canvas and i can´t get to move or scale like i want.why?
Several times i reboot the zbrush because i can´t control the zspheres.
thanks in advance.

http://www.zbrushcentral.com/zbc/showthread.php?t=64774