Well, you can only use RETURN when you have jumped to a routine with GOSUB - NOT when you jump to it with GOTO.

Try:
Code:
Main:
If Switch1 = 1 Then
  Gosub ServoCenter
Else
  Low LED1
EndIf

'And so on...
Goto Main
END

ServoCenter:
'Code here
RETURN

'And so on....
Edit: Oh well, was a bit late there I see....