Nice to know you finally have fixed your issue
Just thought I would throw in my experience, and how I resolved (VC in relation to View Horizon). It's not exactly the same, but may help someone along the way.
Our database was growing too large.
On examining the EVENT tables, we also found login/logouts (slightly different).
Cleanup was a pain, as all space was taken up.
Cleaning out 7 million events at a time would create a massive transaction log, which there wasn't space for.
I ended up doing a query for 1 month of events, and deleting those. Performed DB truncate then Rinse and repeat.
We are running HP Gen 8 servers, so specifically for us, we had this solution (only reported in Jan by VMware):
But of course, we could also just limit the number of events being logged from the VC console:
Administration > vCenter Server Settings > Database Retention Policy > Events retained for x days