Random errors: what can cause them

Deleting twice:
Clearly, deleting a dynamic object twice is a bad idea. But when your code becomes complex, and you need to be able to delete an object from different places, in different cases, you can end up in this situation. The random part here is coming from your code (was it deleted before or not). The error itself appears immediately when you try to delete an object already deleted.

The solution is in that case quite simple: test if the object exists before deleting it. To do that, you need to create a procedure or method in which you trap an exception occurring when you do an illegal operation on a non existing object, like setting it in dynamic object pointer...

Of course, it would be better to always know that an object exists or not, but we all leave in the real world, don't we?