Asteroid 2005 YU55 is now included in the Starry Night data update. So, please update your data file through the program (go to the LiveSky drop down menu and select Update Data Files) then search in Find for "2005 YU55" - and change FInd Objects Whose Name to "Contains" (above search field).
If you are having difficulty finding asteroid 2005 YU55 after updating the data files please do the following: On PC: Look in the Starry Night folder ---> Sky Data folder ----> find the Asteroid.txt file and delete it. Start Starry Night ---> Download data updates ---> Search 2005 YU55. On Mac: RIght click Starry Night application ---> Show Package Contents ---> Contents ---> Resources ---> Sky Data ---> find the Asteroid.txt file and delete it. Start Starry Night ---> Download data updates ---> Search 2005 YU55.