hair modifier problem

i got a problem i have hair modifier(grass) in cycles render. I can see it in material view and in solid view but when i press render grass(hair) desappears.

What blender version ?
Are you using gpu rendering ?
In blender 2.68 try using gpu and the feature set at Experimental
In Layers settings have you enabled ‘Use hair’
Have you read the manual

Attach or post a link to your blend file

it worked when i changed to experimental.
thanks :smiley: