When you create a new build definition, you have the option to create a bug when the build failed.
If you activate this option, it is possible that you will receive the following error message when resolving the bug: The field ‘Assigned To’ contains the value ‘[DefaultCollection]\Project Collection Service Accounts’ that is not in the list of supported values."
The reason for this is that the new build system uses a service account to create the bug, which is a group in TFS. In WIT however we have made a change recently which doesn’t allow to assign work items to groups anymore. We are working on a fix for this, but you can already unblock yourself today. In the build definition, you can specify an explicit value for the System.CreatedBy field.
Sorry for any inconvenience that we have caused.