I am having a problem installing Dropbox in Ubuntu 12.04
Files in subdirectories of /var are locked preventing the completion of installation
Install and run synaptic package tool:
Find via filters drop
There could be one of two issues with this.
1) You may not be running the installer as root.
2) You may have another package manager or installer running, or a broken APT.
If you do have a broken APT and you are sure you have exhausted any other option, try removing the lock and doing a reconfigure by doing:
This should remove the lock and reconfigure dpkg, so you should be able to install again. be careful not to shut down your PC while installing something via APT again.