Try this, it worked for me, although I substituted "NETWORK" for "REMOVABLE" for my test purposes.
#include <GUIConstantsEx.au3>
Local $var = DriveGetDrive("NETWORK")
GUICreate("Test", 230, 60)
$com = GUICtrlCreateCombo( "", 10, 10) ;Create combe
For $d = 1 To UBound($var) -1 ; Set data
GUICtrlSetData( -1, $var[$d] & "|")
Next
GuiSetState()
While 1
$msg = GUIGetMsg()
If $msg = $GUI_EVENT_CLOSE Then ExitLoop
WEnd