Help!! to get text in my Hook : CALLWNDPROC()

Hi,
   In my DLL :

   I use the SetWindowsHookEx(WH_CALLWNDPROC,CallWndProc, ..., 0 ) to Hook the text data in mesage WM_SETTEXT ...

   In the CallWndProc function....  I want to copy out the text data....
   But I just can't get those text.... even I have got the right text data in the CallWndProc funtion by using some DC to output the Text...

   But in otherplace(except the CallWndProc) of the DLL, I just can't get the right text data... why ??
   Is there any constraint in the CALLBACK CallWndProc function ??

   Why can't I get the correct text in other place in my DLL , even APP ??

   Is there any solution ??
   I have tried all the solution of IPC ( eg. send message, copy to global variable, external variable, even file ). I doubt that whether the CallWndProc have set the function( copy data to any memory) off.

   Thank you so much .....