Rigging and Animating for Games - MASSIVE issues

Hey everyone.

I am rigging and animating a model for a game, unfortunately after it has been exported as a .dae file and then imported into FlashDevelop, the animation does happen at all and it makes the model look as if it has exploded (majority of vertices are pulled into one central area).

It seems to be re-ordering the bone structure and this seems to be tripping it up (i.e. Even if the “root” bone is at the top of the hierarchy it seems to be taking in other bones as above that). The model works when it has no animation (not exploded).

It also works when there is just one single bone (animation shows up and everything), but any more than that and it explodes again (and nothing moves).

I am wondering if there is a specific way that you must rig in order for this to come out correctly? Or do you need to delete the armature modifier? And if so is there any way to delete this whilst still keeping the animation?

Any help would be fantastic. I have tried so many different variations but nothing is working.

Cheers!

Please, does anyone know any fix that might be possible?
Or a specific way that you need to rig in order to get this to work?