Unable to Build with the new TfvcTemplate.12.xaml - templates

Question

I tried to used the new template TfvcTemplate.12.xaml with my Builds (Vs 2013) but each time I received the following error message :
TF215097: An error occurred while initializing a build for build definition \path\Buildname:
Exception Message: One or more errors occurred. (type AggregateException)
Exception Stack Trace: at System.Threading.Tasks.Task`1.GetResultCore(Boolean waitCompletionNotification)
at Microsoft.TeamFoundation.Build.Client.FileContainerHelper.GetFile(TfsTeamProjectCollection projectCollection, String itemPath, Stream outputStream)
at Microsoft.TeamFoundation.Build.Client.FileContainerHelper.GetFileAsString(TfsTeamProjectCollection projectCollection, String itemPath)
at Microsoft.TeamFoundation.Build.Client.ProcessTemplate.Download(String sourceGetVersion)
at Microsoft.TeamFoundation.Build.Hosting.BuildControllerWorkflowManager.PrepareRequestForBuild(WorkflowManagerActivity activity, IBuildDetail build, WorkflowRequest request, IDictionary`2 dataContext)
at Microsoft.TeamFoundation.Build.Hosting.BuildWorkflowManager.TryStartWorkflow(WorkflowRequest request, WorkflowManagerActivity activity, BuildWorkflowInstance& workflowInstance, Exception& error, Boolean& syncLockTaken)
Inner Exception Details:
Exception Message: VS30063: You are not authorized to access http://tfs.mydomain.com:8080. (type VssUnauthorizedException)
Exception Stack Trace: at Microsoft.VisualStudio.Services.Common.VssHttpMessageHandler.<SendAsync>d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1.ConfiguredTaskAwaiter.GetResult()
at Microsoft.VisualStudio.Services.WebApi.VssHttpRetryMessageHandler.<SendAsync>d__1.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Runtime.CompilerServices.ConfiguredTaskAwaitable`1.ConfiguredTaskAwaiter.GetResult()
at Microsoft.VisualStudio.Services.WebApi.HttpClientExtensions.<DownloadFileFromTfsAsync>d__2.MoveNext()
I tried to find an answer with the error code, but nothing seems to be linking on my problem. Could you help me? :)
Thanks