Try to send characters instead. This should work with most controls.
Function SendCharactersToWindow
See also: SendKeysToWindow
Function SendCharactersToWindow
;/
function hwnd $_string
;Sends the string to a child window using WM_CHAR messages.
;The window can be inactive.
;hwnd - child window handle.
;EXAMPLE
;int hwnd=id(15 "Notepad")
;SendCharactersToWindow hwnd "Line1[]Line2"
str s=_string
s.findreplace("[]" "[13]")
s.unicode
word* w=s
for(_i 0 s.len/2) PostMessageW hwnd WM_CHAR w[_i] 0
See also: SendKeysToWindow