Ok. It seems that the issue is anywhere within the datamodel - maybe there are now any synthetic keys, circular loops or broken associations (and loosen tables) or something like that through any changes on the load-steps before. Therefore I think you should open the application with the desktop client and find and fix the issue.
Another possible reason could be that there is an issue with server-objects which are stored within the shared-files. For checking you could just remove the shared-file (I would backup it before) and then test again. If then the application reacts normal you could try to restore an older version of them and/or to repair them with the Power Tools 1.2 for QlikView.