So I rewrote the skript to support the players, but it still showed the error.
if arg-1 is "create":
if arg-2 is set:
if {clan::%player's uuid%} is not set:
set {_1} to length of arg-2
if {_1} is less than 15:
set {clan} to arg-2
send "&aClan created: %arg-2%"
broadcast "&a&l%player% &a&lcreated the clan %arg-2%&a&l!"
set {clan::%player's uuid%} to arg-2
add player to {clanplayers::%{clan::%player's uuid%}%}
else:
send "&cEither A: You already have a clan, or B: You didn't type a name" to player
if arg-1 is "tag":
set suffix of {clanplayers::%{clan::%player's uuid%}%} to " &a[%arg-2%&a]"
send "&aClan tag set to %arg-2%&a."