Is data collection failing with Java Heap space out of memory.
There are a few ways to increase memory allocations for the webgui/corbaserver/java components if you getting the above errors.
Have you examined the core logs for additional errors?
Does the entry for the OPSCentre server still exist in the Master Servers bp.conf file.
Did you make use of Host entries maybe on the master server, it could just be a name resolution problem.