TF215097: An error occured while initializing a build for build definition - tfs

Question

We just installed TFS2013 Update 2 on a brand new server with server 2008 r2 on it. At one moment in time I was able to run builds for my projects but now I can't and I don't know why or what even changed. The explination will get a little winded so sorry. Here is the full exception that i see every time. All of my projects use the CMMI process, so out of curiousity I made a new project called Hello World Test that uses the Agile template. Made a new build, committed my code and sure enough just like all my other projects I get this error. There are 3 accounts in our TFS server, 2 are admin and 1 is a contributor. I'm one of the 2 admins, but both of us have same problem. I've even logged on as the system admin and tried kicking off a build and got same error.
TF215097: An error occurred while initializing a build for build definition \Hello World Test\WpfApplication1:
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://foo.bar.com:8050. (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()
After getting this error about 100x I checked the Application logs to see if i could glean any sort of information and the only thing I could see was that during creation of the build server was this Failed to add the build service account 'CORP\Administrator' to Windows Group 'IIS_IUSRS'. Details: Group does not exist. I tried changing the build server user and each time i get the same Warning message in the event logs. I'm almost 100% sure this is the problem. Now what I find odd about this particular error is that I can see IIS_IUSRS in active directory but i keep getting that error. Anyone have any clue as to why i'm getting this error? What information can I get anyone to help figure this out?