It appears that something has changed between r13040 and r13060 regarding the final build of the firmware image file when building for an Atheros 231X based Ubiquiti Nanostation 5. The '~bin/openwrt-atheros-ubnt5-jffs2-64k.bin' file is never generated. It used to be generated automatically from the '~bin/openwrt-atheros-root.jffs2-64k' and '~bin/openwrt-atheros-vmlinux.lzma' files (which are built). Has the philosophy as to whether or not to create this file changed, or is this a bug?
Here's output from make V=99 from a clean svn checkout of r13088 showing the problem.
It turns out the mkfwimage error was generated indirectly from performing a build that exceeded the flash size of the target device. Mkfwimage does some error checking and proceeds to throw an error rather than generate a ".bin" file if a user inadvertently exceeds the capacity of the target device. This Ticket has no need for further resolution.