Installing tomcat 7 on Ubuntu Server 12.04
Solution 1:
This is because the package tomcat6-common is still residing in the system.
do this
sudo apt-get remove tomcat6-common
This will remove the conflicting package. Installing Tomcat7 Should work fine now
Solution 2:
I had the same problem and I haven't tomcat 6 installed on my system before.
I fixed it by manually installing libtomcat7-java. (At first I want to install tomcat7-common manually and it complains about libtomcat7-java)