There is no way to know specifically which object has the problem, you need to figureout what object can be, talking with the users with privileges to create shared objects, maybe for the title of the object, must be very slow object, after that looking in the management console by user and by the title and you can delete the object there....
Use the QV Power Tools "Shared File Viewer"
to identify the large chart. Then use the QEMC to server objects pane to delete the chart object. You won't see the shared file get smaller until you use the Defrag funnction in the Shared File Viewer to release the unused space.
I recommend that you work on a copy of the shared file -- not the file in use on the server.