_Trev_ posted this in the other thread. Worked for me when I did it using iFuntastic.
Download this (from Rapidshare) http://rapidshare.com/files/54783302/youtubescript.zip.html and decompress it.
1) Using your FTP program go into the following folder on your iPhone "var/root/Library/Lockdown/" and drag the following three files from the folder above into it: "data_ark.plist", "device_private_key.pem", "device_public_key.pem" (Overwrite the files when asked.)
2) Now go to the following folder "/usr/libexec/" and copy this file "lockdownd" (Again overwrite when asked.
3) Finally go to this folder "/var/root/Library/Lockdown/" and delete the "activation_records" folder within that folder. (Or just the .plist file inside)
4) Restart your iPhone and YouTube should work.