In a sense, I don't blame the OP in this case (despite blindly clicking through and/or ignoring the given warning).
Even though it is necessary to specifically tell RbUtil to display the disabled targets, in the case of the Classic, especially if you have no experience with this device and Rockbox, I suppose it would be non-obvious that one must first install a bootloader from a entirely separate project that the utility makes no mention of, and that RbUtil is incapable of installing said bootloader (or that this is even required).
[Saint]