If you have RM_OLD_IMAGE = "1" set and then delete the actual image file but leave the latest symlink in place, the next time you try to build the image do_rootfs will fail with a traceback (see attached). The code should just skip deletion if the target file doesn't exist.
Created attachment 1851 [details] Failure log
Patch merged: http://git.yoctoproject.org/cgit.cgi/poky/commit/?id=5b594449f73f6cff99695119eb00ee5dcc672aed