I can confirm this bug on OSX too, the log file indicated a null reference exception in TweakScale (sorry I don't have the log, but can be reproduced easily). I've isolated it to ModuleManager (2.1.5). Reverting to 2.1.4 resolves the issue. As there was only a one line change for version 2.1.5 (if (nodes.Length == 0) return null;) I suspect this is what is causing the null reference . I believe this is still a bug which needs to be resolved in TweakScale. You can download the previous ModuleManager at https://github.com/sarbian/ModuleManager/releases