For any reason one of my Windows 10 Enterprise PC don't offer the update 1511.
I suppose that the update failed.
I can download the new ISO Image from my MSDN account. Is this the correct way to install the update via DVD to download this image and start the update from this DVD ISO image?
PS (after the question was answered): I have the problem with more than 1 PC. I have installed the MSDN Windows 10 Enterprise version. Currently I detected 3 Laptops/PCs that don't offered the update. All Windows 10 Home machines got this update.