That's an error related to Directx (the underlying software DDO and many other software programs rely on for multimedia and graphics). Did you change anything graphics or sound or mouse or anything related on your PC?
First, in my opinion you should restart your system just to make sure the problem doesn't fix itself.
Then, there's an article in the Turbine Knowledge Base about this, go to
http://support.turbine.com and type "dinput8" into the search box at the top left and click SEARCH. Follow the directions in that article.
See if that helps...