On newly installed or existing NBS server, PXE configurations fail to properly build to SBS. NBS agent logs show 'Configuration failed' with return code 27
In one instance of this issue, it was reported that Windows Security logs on the NBS server were full of Audit Failure Event ID 4656
Deployment Solution 8.5 RU1
In one instance of this issue, it was discovered that a non-default GPO was applied to the NBS server.
The following GPO was reported as being disabled:
'System objects: Require case insensitivity for non-Windows subsystems'
Setting 'System objects: Require case insensitivity for non-Windows subsystems' to default 'Enabled' resolved this issue.
There may be other causes of the error code but this is one possibility