Hi,
It's really hard to tell anything from code snippets like this. Can you duplicate the problem in a small sample project? If so, you should Submit an incident to Infragistics Developer Support and they should be able to tell you why it's not working.
Your mention of AfterCellUpdate is interesting. Are you calling Refresh while there is a cell in the middle of an update? If that's the case, then that might be the problem. To test that theory, you might try calling PerfromAction(ExitEditMode) on the grid before you call Refresh and see if that makes any difference.