Data Usage Warning in ICS I found these related questions on the same issue:


How do I disable the data usage warning and notification in ICS?
How to turn of Google Samsung Nexus Galaxy 3g/mobile data usage warning?


But, my problem is the graph doesn't show up the limit lines. How to disable the notification now? 

 
Screenshots (click for larger variants)

When I try to set mobile data limit I'm getting the message from the second screenshot and it backs to the first image. It is not enabling.
I fixed it editing the netpolicy.xml file manually. Increased the warning limit to 4GB in 3 places as shown in the image and rebooted. Then the notification went-off:


Remount /system to make it writable (mount -o remount,rw /system)
Edit /system/netpolicy.xml file as root:

Remount /system read-only (mount -o remount,ro /system) or reboot the device