After trying to use this combination on a site I was building for a client (I am a designer, not a programmer), I can get the events to save to the calendar in the back end, but the calendar shows no events. This is on a clean install, r108 of Event Calendar and r395 of DataObjectManager.
There are no other modules, and it is using the default theme (I was trying to see if it was my custom page types causing a conflict - it isn't them, because they aren't there).
There are no errors, nothing. Just no events in the upcoming events (or on the calendar).
Hey maryfran, Your purpleurbia site got me motivated to work with Silverstripe. Now12 forum threads in the Silverstripe forums, I was able to launch about three web site projects. I got the events calendar working fine in one of them: calfitnesscenter.com.