mov eax,offset buf
   invoke lstrlen,eax  
  mov ebx,offset buf
 add ebx,eax     
again:        
dec ebx      
cmp ebx,'\'   <-------------???    
jne again      
inc ebx

mov ofn.lStructSize,SIZEOF ofn
push hDlg  				
pop  ofn.hWndOwner
push hInstance  				
pop  ofn.hInstance
mov  ofn.lpstrFilter, OFFSET FilterString
mov  ofn.lpstrFile, OFFSET buf
mov  ofn.nMaxFile,MAXSIZE
mov  ofn.Flags, OFN_FILEMUSTEXIST or \ OFN_PATHMUSTEXIST or OFN_LONGNAMES or\ OFN_EXPLORER or OFN_HIDEREADONLY
mov  ofn.lpstrTitle, OFFSET OurTitle
invoke GetOpenFileName, ADDR ofn