When you 'select' you select from an array. if you have a variable, object or what ever one piece thingy you can't 'select' it because there's nothing to select from. As for an array the case is opposite. An example
you want a script to select _weapon from an array you'll first have to define the array
m16 is not an array
[m16] is an array
if I'm reading you right you're executing a script or something? Passing info to the script when executing it must be done inside an array, so you could have
dude,m16 exec "myscript.sqs"
_myguy = _this select 0
_weapon = _this select 1
That wouldn't work
[dude,m16] exec "myscript.sqs"
_myguy = _this select 0
_weapon = _this select 1
Would work because the passed info is inside an array where the selection can be made