You will need to re-lock your Titan prior to flashing the stock 2.17 ROM.
ftp://ppcgeeks:ezupload@ftp.ppcgeeks...n_Relocker.exe
In the future, it would be a good idea to read everything you can find about flashing a new ROM, have all necessary files downloaded, and also read about the problems others have encountered, and the fixes they employed, PRIOR to starting the flash yourself.