Problem with pcap library


I want to work with the pcap library, and I installed libpcap and pcap
library in Ubuntu, but when I try a code, there is an error:

//var/lib/gems/1.8/gems/pcap-0.7.1/lib/pcaplet.rb:67:in initialize': uninitialized constant Pcap::Pcaplet::PcapError (NameError) from tcpdump.rb:14:innew’
from tcpdump.rb:14

I searched on the net i didn’t find anything to help to pass this error.

Thanks in advance