This question has been answered by BobRay. See the first response.
Go into the database in PhpMyAdmin. In the modx_dashboard_widget_placement table, delete all the records. Be careful about the table name - the table should have only three feilds: dashboard, widget, and rank.
That won't affect the widgets themselves, but it will remove them from all dashboards. You can put them back later. Re-install UpgradeMODX before putting it back on a dashboard.
Are you saying that deleting the records in the modx_dashboard_widget_placement table didn't work? I believe it would have if you cleared the cache files.
Which widget did you delete?
That's very odd. With no records in the placement table, UGM was not on any dashboard and should never have executed unless the dashboard placements were in the MODX cache.