You are using an old version of the channel. The tutorial probably provided old files. (old tutorials are not very good to follow)
OR maybe you installed boot.dol inside priiloader, which is another reason why AHB is not available to you. But as you asked for the updated files I guess you have an outdated channel.
You can find latest files here :
latest USBLoaderGX program :
http://www.mediafire.com/download/m32kjd1444k709q/R1259.7z
Latest USBLoaderGX channel :
For Wii and for
WiiU vWii
(it's the forwarder, the full channel is outdated and not maintained anymore)
place the latest program on your SD (or usb, but sd is recommended)
Remove your current channel (using the same wad you used to install it and a wad manager in "uninstall" mode)
install latest forwarder.
Do not install USBLoaderGX boot.dol inside priiloader's autoboot menu.
Latest program is always in my signature, and from time to time I also release it in the internal updater (you get an update message when launching the loader if you enable network auto-connect option).
By using the forwarder instead of the full channel, it's easier to update : replace the boot.dol on SD card. no need to reinstall another channel.