Question

Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following package was automatically installed and is no longer required:
  libruby1.8
Use 'apt-get autoremove' to remove them.
The following extra packages will be installed:
  xserver-common
The following NEW packages will be installed:
  xvfb
The following packages will be upgraded:
  xserver-common
1 upgraded, 1 newly installed, 0 to remove and 308 not upgraded.
1 not fully installed or removed.
Need to get 0 B/899 kB of archives.
After this operation, 2,068 kB of additional disk space will be used.
Do you want to continue [Y/n]? Y
Setting up apt (0.8.16~exp5ubuntu13.2) ...
gpg: symbol lookup error: /usr/local/lib/libreadline.so.6: undefined symbol: UP
gpg: symbol lookup error: /usr/local/lib/libreadline.so.6: undefined symbol: UP
dpkg: error processing apt (--configure):
 subprocess installed post-installation script returned error exit status 127
Errors were encountered while processing:
 apt
E: Sub-process /usr/bin/dpkg returned an error code (1)

Why I cannot install xvfb?

Answer 1

Get your admin to run this:

su
mkdir temp
mv /usr/local/lib/libreadline* temp
ldconfig 
apt-get update

Then run your apt-get again