We have had a major issue for something like 6months now.
I am pretty sure its our codes fault but I have had some difficulties of finding the issue.

When I alt tab from fullscreen or change the resolution in game
it always gives an error message like this:

---------------------------
Error
---------------------------
Can't set new display mode: RESET_DEVICE_RESET_FAILED
Can't set old display mode: RESET_DEVICE_RESET_FAILED
---------------------------
OK
---------------------------

Any suggestion where to look around on an error like this would be helpfull.

Image_rt render targets not released as in tutorial?

Hmm,.. can you be more specific.. Which tutorial is this?

31 - Render To Texture.cpp

D.lost=Lost; // specify custom function called when D3D Device is lost

Do you mean this one?

Yeah this must be it.. Im sure this will correct the problem. Thank you..

yes