Encountered a similar problem a few weeks back... Seemed to result from element level corruption, and corrupt elements being deleted from the Central Model.
If you are not able to open a new local copy, or the Central Model directly, are you able to open any of your users existing local files directly? In my case, I was able to open a recent local file, and then use it to re-create the Central Model. The local file was recent enough that no significant amount of work was lost.