It’s a small issue, you may encounter if you name your build definition with the same name as an old one.
Here is the error
Exception Message: Unable to create the workspace ’80_6_tfs2bld’ due to a mapping conflict. You may need to manually delete an old workspace. You can get a list of workspaces on a computer with the command ‘tf workspaces /computer:%COMPUTERNAME%’. Details: The path C:Builds6Windowssrc is already mapped in workspace 77_6_tfs2bld. (type MappingConflictException) Exception Stack Trace: at Microsoft.TeamFoundation.Build.Workflow.Activities.TfCreateWorkspace.Execute(CodeActivityContext at System.Activities.CodeActivity`1.InternalExecute(ActivityInstance instance, ActivityExecutor executor, BookmarkManager bookmarkManager)
at System.Activities.Runtime.ActivityExecutor.ExecuteActivityWorkItem.ExecuteBody(ActivityExecutor executor, BookmarkManager bookmarkManager,