It really looks like Samsung's Windows Phone 7 devices are causing some trouble. First, the pre-NoDo updates for the Samsung Omnia 7 and Samsung Focus were paused and now it seems the Windows Phone security fix (May Update) causes some further problems to be rolled-out via Zune - which is Microsoft's preferred method to update Windows Phones. However, doesn't matter if Zune is the preferred method or not, it's always possible to flash a Windows Phone 7 with manufacturer utilities and Samsung has just released a so called "Device Update Tool for Omnia 7" which helps to flash the Windows Phone security patch, in case users have noticed "Error Code 801812C1" while trying through Zune.
It's definitely advised to try out Samsung's Omnia 7 Support Tool only, if the regular update via Zune failed, because it's not said that all carriers have already rolled-out the May Update. Therefore it shouldn't be used before the updated was tested with Zune.
Nevertheless, if the update failed with the error code above, the Samsung Omnia 7 Support Tool is now available as a free download from Samsung.
Cheers ~ Arne