I've recently installed Ubuntu 12.04 and Wireshark. Due to issues with a video driver I had to install Ubuntu again. Both times I used the following procedure to fix the permissions issues with Wireshark:

http://tryout-chen.blogspot.com/2011...capturing.html

After following the procedure and logging out/in Wireshark runs without error and I can capture on my Ethernet and WiFi interfaces.

Good luck!

Colo993