ping destination host unreachable on ubuntu 11.04

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http://askubuntu.com – I have set up an Ad-Hoc on one of my laptop1(ubuntu 11.04), another laptop2(ubuntu 11.04) also connected to the same ad-hoc. However, when I ping both of them. The result shows "Destination Host Unreachable". I don know what is going wrong. Any help? (HowTos)