I modified a theme this morning and after changing a property got the error: "There are errors in SASS and it cannot be compiled to CSS.". Changing the property back to what it was before did not resolve the problem. Clicking the Undo button over and over and over did not resolve it. 

I started over with a backup taken yesterday and started reapplying changes. When I clicked "Export All" I once again got the same error. There is no way to recover from it. 

I've had ThemeBuilder licensed for some time, but this is the first week I've tried to use it in our application. It seems to be total garbage. I can't see any why forward with us using a tool that's going to randomly produce unrecoverable errors.