If a job is configured to use Slack to send "Notify Build Start" notifications and also uses the TFS source control plugin, this exception is logged in the build output:

FATAL: getAffectedFiles() is not implemented by this SCM
java.lang.UnsupportedOperationException: getAffectedFiles() is not implemented by this SCM
at hudson.scm.ChangeLogSet$Entry.getAffectedFiles(ChangeLogSet.java:242)
at jenkins.plugins.slack.ActiveNotifier.getChanges(ActiveNotifier.java:151)
at jenkins.plugins.slack.ActiveNotifier.started(ActiveNotifier.java:86)
at jenkins.plugins.slack.SlackNotifier$SlackJobProperty.prebuild(SlackNotifier.java:307)
at hudson.model.AbstractBuild$AbstractBuildExecution.preBuild(AbstractBuild.java:834)
at hudson.model.AbstractBuild$AbstractBuildExecution.preBuild(AbstractBuild.java:829)
at hudson.model.AbstractBuild$AbstractBuildExecution.preBuild(AbstractBuild.java:825)
at hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:534)
at hudson.model.Run.execute(Run.java:1741)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:43)
at hudson.model.ResourceController.execute(ResourceController.java:98)
at hudson.model.Executor.run(Executor.java:408)
Skipped archiving because build is not successful
Finished: FAILURE

See this link for a similar bug (and a fix) that affected the hipchat plugin:

https://github.com/jlewallen/jenkins-hipchat-plugin/pull/60

The workaround is to disable the "Notify Build Start" option for the Slack plugin.