I am having a similar issue;

Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 ajenti : Depends: python-requests but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
root@lagrange:~# apt-get install python-requests
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 python-requests : Depends: python2.6 but it is not installable
  Depends: python (< 2.7) but 2.7.3-0ubuntu2.2 is to be installed
  Recommends: python-gevent but it is not going to be installed
  Recommends: python-oauthlib but it is not installable
E: Unable to correct problems, you have held broken packages.
root@lagrange:~# apt-get install python
Reading package lists... Done
Building dependency tree
Reading state information... Done
python is already the newest version.
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
root@lagrange:~# python-requests

Fresh Ubuntu 12.4.2 LTS Server install

Any suggestions