Actually if I understand END I know why it fails, the function it will call depends on a lot of modules the main one has loaded, and since end is run when the module finishes in order the other modules end and go away before the END is called for this module.

That's not how END works; END blocks run in a deterministic manner, and they run before a module "goes away", whatever that means.

We'd have to see code before diagnosing any problems.