Impossible to transfer cbz or cbr on any reader.

Hi everyone.
So here it is. Calibre is an old friend since years, but there. It has a problem I can't solve alone. Hope a good soul can give me an answer to this.

Whatever reader I connect, I can transfer epub, pdf or whatever the readers can read with no problem, except when it comes to cbr or cbz stuff.
Each time I try to transfer a cbr/cbz file calibre shows me a box saying the format is wrong and asks me if I want to convert it.
But I don't want to convert. I bought my readers for cbz and cbr support and to have not to convert to pdf or epub anymore.
How can I simply tell Calibre just to transfer it on my reader ?

Thanks for all the help you can provide me.