Its the .dll libraries which the lotro update screws up by the look of it.
Go into your install directory for DDO (in my case it was: 'C:\Program Files\Turbine\Dungeons & Dragons Online - Stormreach').
Execute the 'TurbineRegisterGDF.exe' program you see there and press the confirmation buttons as they pop up. If you have been messing around running the lotro/ddo clients you may get a message saying that one of the .dll libraries cannot be uninstalled properly. Don't worry about it.
Restart DDO launcher, and let it get updates (if necessary for you).