We are trying to use the new labeling feature in teamcity 9.0.2 I have gotten this working for java builds on a linux build agent with ssh authentication to our github enterprise. This error mesage is from a .net build on a windows build agent. I think the difference is that the .net build is using jgit and not regular git. I have tried checking out the code on the teamcity server and on the agent but see no difference. We are also not using refs/heads/master, we are using a branch called test and using refs/heads/test. Also we are using ssh authentication and https is not configured. Maybe this feature use https for .net?