Error in virtualbox ubuntu whilst attempting to fix screen resolution

Question

When I try to fix my screen resolution using techniques listed here get an error:

E: Could not get lock /var/cache/apt/archives/lock – open (11: Resource temporarily unavailable)
E: Unable to lock directory /var/cache/apt/archives/

Answer 1

The error means that a package manager (e.g. apt-get) is currently running and locking mentioned files and directories. Try to find the process and end it regularly (if possible) or just restart your computer. Afterwards the lock should be remedied.

Answer 2

This means you are attempting to use apt simultaneously with two different processes. Most likely you have the software center or synaptic open while you are installing/uninstalling stuff on the terminal. To prevent major conflicts, apt can only be accessed by one process at any given time.

Please close the multiple processes attempting to access apt (most likely software center and synaptic).