Hi, thank you for the response.
After reading your replies and doing some more research I removed the dispose of the object given in the event argument.
My reasoning is that, because I (any of my commands) did not create the object, I should not dispose of it.
Details:
In this case, it was an Xrecord that was appended to the database by autocad. In the HandleAppendEvent, I look at the object, and if it is for example a polyline I would do stuff with it.
I used to believe that, because I accessed the object, just to be sure, I needed to dispose it.
But in case of the Xrecord, me disposing it, made it unavailable to autocad, which was still busy with it. Resulting in a read/write exception and autocad crashing.