I don't really know. I am sorry. I guess it has something to do with the try of the GPU to access to a deleted buffer but no idea why and when could it happen. A resolution change is conflictive because everything has to be rebuilt from scratch after resizing the device backbuffers. I would try to avoid it as much as possible. Have you got more cameras around? Has any entity or material a rendertarget linked for shading?

You might try to set a larger bmap_zbuffer from the very beginning so the rendering target is not resized, just its viewport... I hope