when does occur this crash report?

I got this crash report from my app, and I can't reproduce it as I don't know when it happens and how can happen. Someone can tell me what sees from this report?

Code:

Error Name: NilObjectException
Error Number: 0
Error Message:
Stack Trace:
RaiseNilObjectException
ConScheduler.ConScheduler.StyleGrid1_DropObject%%o<ConScheduler.ConScheduler>o<DragItem>i4
_Z17UpdateMouseCursorv
Delegate.Invoke%%
App开发者_运维百科lication._CallFunctionWithExceptionHandling%%o<Application>p
_Z33CallFunctionWithExceptionHandlingPFvvE
_Z8mainloopv
RuntimeRun
REALbasic._RuntimeRun
_Main
% main

Regards, Pentium10

Based on the text, you might want to check out your usage of the Einhugur StyleGrid. It appears the NilObjectException came from there.