Converted to raw, but format is now qcow2 ????

I downloaded an image in IMG format and converted it to QCOW2 using "qemu-img convert" command. When I wanna lunch an instance based on this QCOW2 image, I face with the following error: **Build of instance xxxxxxxxxx aborted: Image yyyyyyyyyyyyy is unacceptable: Converted to raw, but format is now qcow2** What's wrong? Thanks