the X2 5035 bios has two versions, an 'old' version for v1.0-1.5 xboxes, and a '16' version for v1.6 boxes such as yours. Did you flash the right one? Also, how did you fkash the bios in the first place? you either need to transfer both the 'x2_5035_v16plus_512k.bin' file and 'config.ini' file to the root of your E drive (via FTPing into yor box whilst booted into Xenium OS), or you need to burn a copy of the x2_5035 bios to disc and find it in the D drive during the flash process. Also, the file should be a '.bin' file.
i recommend you get 'The Iceguide' and give it a read. It'll take you through all the steps of properly flashing a bios as well as all the downstream dashboard setup (which you'll also have to do before you can do anything with your chipped box).
Also, if the error message you get is '05', means you're trying to launch teh MS kernel with an unlocked HDD, needs to be locked. I recommend though leaving the HDD unlocked whereever possible. Only lock it when you need to use the MS bios, such as if you want to play xbox live.