Interface not supported

[M.E.]

Some months ago I started getting Ole Errors while trying to manage Excel
from Delphi 5 under Win2000.
Well, I cleaned my HD, reinstalled Win2000, D5 and Office 97. After
recompiling
my app I am getting that it "raised exception class EIntfCastError with
message Interface Not Supported".

type
ExcelApp: TExcelApplication;
var
WB: TExcelWorkbook;
begin
ExcelApp.Visible [0] := True;
WB := TExcelWorkbook.Create(Self); <= ERROR HERE

I traced the OleServer unit and found the error is raised here:
ComObj.InterfaceConnect(Obj, FServerData^.EventIID, FEventDispatch,
FEventsConnection);

The application * still run under Win98 *, but raises that error under
Win2000.
No one at the Borland newsgroup had any idea. Does anyone here? What is
missing?
Thanks,
Marcio