GetDlgItemTextW/SetDlgItemTextW do not want working

[antarctidaonline]

I write a simple demo dialog-based application. I use Windows 7 x64 and ml64 from DDK 7600.16385.0. Dialog box has button ID_READ, edit control ID_DIAM and static control GLAND_LAB. I want to get text from edit control and set text to static control. I wrote small C application with such dialog procedure:

long long int __stdcall DlgProc(HWND hWnd, unsigned int i1, unsigned long long int i2, long long int i3)
{
const wchar_t string1[BUF_SIZE];
if (i1 == WM_COMMAND)
	if (i2 == ID_READ)
	{
		GetDlgItemTextW(hWnd, ID_DIAM, (wchar_t *)&string1,BUF_SIZE);
		SetDlgItemTextW(hWnd, GLAND_LAB, (wchar_t *)&string1);
	}
return 0;
}

and tested it - works well.
Then I wrote such assembler code:

dlgproc proc
	push rbx
	sub rsp, BUF_SIZE*2+20h
	mov String, rsp

	xor rax, rax
	mov hDlg, rcx
	cmp rdx, WM_COMMAND
	jne NoCommand
	cmp r8, ID_READ
	jne NoCommand

	; Get text:
	mov r9, BUF_SIZE
	mov r8, qword ptr [String]
	mov rdx, ID_DIAM
	call qword ptr [__imp_GetDlgItemTextW] ; access violation here!!!

        ; Set text:		
	mov rcx, hDlg
	mov rdx, GLAND_LAB
	mov r8, qword ptr [String]
	call qword ptr [__imp_SetDlgItemTextW]
	jmp NoCommand

        ; out code:
NoCommand:
	add rsp, BUF_SIZE*2+20h
	pop rbx
	ret
dlgproc endp

And this code causes access violation executing function SetDlgItemTextW. I used debugger WinDbg and checked values of registers rcx and r8 before executing functions GetDlgItemText and SetDlgItemText - they are the same. But first function executes without errors, and second do not want to work. I can not find valuable differences between disassembled C code and my code. Maybe I do not know something?

[antarctidaonline]

I found my mistake. Analysing C disassembled code, I found, that I must replace code

    sub rsp, BUF_SIZE*2+20h
    mov String, rsp

by code

    sub rsp, BUF_SIZE*2+20h
    mov String, rsp
    add String, 22h

I do not know why I have to add some offset to address, but - nothing works without it. What can be cause of it?