function not declaring default variable value?

Hello, I am having a slight problem, do not know if it's an autoit bug or what, but when I try to declare a default value for a function them call it via guictrlsetonevent, the variable is not declared. I have tried pretty much everything I can think of, setting it to default, true, false, numbers, and strings, and it's always the same error.

func _messagego($enckey = "Default")
if not IsDeclared($enckey) Then
$enckey = $activekey
Else

endif
endfunc

 

"Y:\SIM\Networking\outgoing.au3" (4) : ==> Variable used without being declared.:

if not IsDeclared($enckey) Then

if not IsDeclared(^ ERROR