Suddenly can't add virtual servers

Hi,
I recently installed virtualmin and managed to create a virtual server and everything worked fine.
But today, I tried to create a new virtual server and I get this:

Creating administration group hundred ..
.. done
Creating administration user hundred ..
.. done

Failed to create virtual server : **blank**

For some reason, the actual error is blank and so I have no idea what has happened and what I have broken since I added the previous virtual server.

Any Ideas?

Thanks,
Daniel