You didn't follow all of that FAQ post, or you'd have more info for us.
That being said, Don't change superadmin to owner. Ever.
99% of all scripts written for Gmod expect the highest group to be superadmin. FPP is included in that 99%
And the second group to be admin.
Why/where the heck owner group came from I'll never understand,
and it's a bad idea in gmod terms.Either change yourself back to superadmin, or if you deleted it, which means you ignored BIG GIANT LETTERS TELLING YOU IT WAS BAD, then use ulx group reset
"ulx resettodefaults" and make yourself superadmin again.