Return of Reckoning

Error: System.IO.IOException: The process cannot access the file 'D:\Warhammer Online - Age of Reckoning\art.myp' because it is being used by another process.
at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
at System.IO.FileStream.Init(String path, FileMode mode, FileAccess ...