OPC in Matlab (Problem to interface PC <-> PLC)

Hi all!

I have been trying to make a connection to an OPC server using the OPC Toolbox(simulink) but after clicking the "Add Items" button (in Simulink OPC Read block), I get the following error:

??? Attempt to reference field of non-structure array.

Error in ==>
C:\MATLABR2007\toolbox\opc\opcblks\opcmasks\additemdlg.p>dlgAddItem_ResizeFcn at 310


Error in ==> gui_mainfcn at 96
feval(varargin{:});

Error in ==> C:\MATLABR2007\toolbox\opc\opcblks\opcmasks\additemdlg.p>additemdlg at
33


??? Error using ==> set
Error while evaluating figure ResizeFcn


Anyone have any clue what's the problem?