For reasons beyond my head, unlaunch will fail to uninstall on dev units. It sounds like it's something to do with exploitable titles blanking out a register and unlaunch not being happy with it. Thankfully you don't need exploitable titles on dev units!
- Download a DSiWare type homebrew capable of booting an SRL...
Source: https://gbatemp.net/threads/install-unl ... as.648979/