Classifieds not activating properly?

We've been using the classifieds plugin for a while with no problem but this morning we noticed that it seemed to have been deactivated. I checked the plugins list and found that it was still activated but there was no menu item in the back end for classifieds. I've tried deactivating and reactivating the plugin, uninstalling and reinstalling but, although I'm told that the plugin was activated, I'm not seeing any change other than the addition of the 'CustomPress' menu item.
The only thing I can think of that might have caused the problem was an update of Friday causing some incompatibility with the theme or other plugins but I've tried a test site on the same network with different themes and plugins with the same results. I've also checked the error log but there isn't anything in there.

Any help would be appreciated.
thanks