[ubuntu] Intermittent dns failure

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http://ubuntuforums.org – I have a private network 192.168.3 with Ubuntu server 12.04 running dnsmasq for the dns server (dhcp is disabled). Intermittently one of the work stations on the network will make a call to a page on the local server and get back a responce "server not found". The work station may be an xp system or a win 7 system. The responce is the same on either. The only resolution we have be able to find is to reboot the windows system that had the error. This of course is not an acceptable solution. Do you have any ideas where I should be looking? My warehouse staff is getting pretty (Hardware)