Try this
Code:
Dim Secret(StrLength(Nickname)/2) As byte
For i = 0 To ArrayLen(Secret()) - 1
Secret(i) = Bit.HexToDec(SubString(Nickname, i*2, 2))
Next
test1 doesn't show up in your listbox
test2 decodes as "w"
test3 decodes as "e"
test4 decodes as "Arjan"
test5 fails on bad data