"Cannot make a visible window modal"?

Hi,

I'm accessing form2 from my main form1. Form1 uses this method to hide
itself and show form2:

void __fastcall TIDForm::ButAdminShortClick(TObject *Sender)
{
   Application->ShowMainForm = false;
   IDForm->Visible = false;
   Admin ->ShowModal();
   IDForm->Close();

Quote
}

Then Form2 can get back to Form1 by using this:

void __fastcall TAdmin::ButLogoutClick(TObject *Sender)
{
        Application->ShowMainForm = false;
        Admin->Visible = false;
        IDForm->ShowModal();
        Admin->Close();

Quote
}

Now if I use the method to access Form2 again, I get the error:

"Project Project1.exe raised an exception class EInvalidOperation with
message 'Cannot make a visible window modal'. Process stopped. ..."

Been stuck with the Builder help file for 3 hours now with no success,
hopefully someone here has a hint or an answer.

TIA

/Chris