Simple errors, like freeing an already-freed entity, are normally caught by the engine and will not cause a crash. If the error is not obvious, it could be something more sinister, such as something overwriting some internal memory areas.

For finding the reason of such a problem, reduce your application step by step until the crash disappears. First remove all external plugins, then disable all functions that access internal memory structs, then remove all effects. If then the problem still is there, send me that project and I'll look into it. I'm meanwhile sort of an expert in finding hidden bugs in user projects.