Invalid fixed string

[jarovo]

I am trying to follow https://fedoraproject.org/wiki/Using_Yubikeys_with_Fedora#What_is_modhex.3F

sudo ykpersonalize -1 -ofixed=vvBgkeNvlUBc4Cio -ouid=jhenner -aa7eb350182ab3acf32a14616fc73b087  -oappend-cr  

gives an error Invalid fixed string. I don't understand why. When I use the same value as in the fedoraproject manual, I get the similar message, but about the uid. I don't understand how to set it. The page on fedoraproject doesn't help. Nor does any manual I found. Please help and please update the manuals.

Thanks