XPInstall callback() function problems !

Hi !

I use the InstallTrigger.install() function inside my javascript code. Here
the code:
...
  var xpipackage = {'mySample Installation':'XPInstall.xpi'};
  InstallTrigger.install(xpipackage, xpinstallCallback)
...

Also I have definded a function called xpinstallCallback(url, status).

This function is also called by XPInstall but I have problems to solve the
status.
Here the function:

function xpinstallCallback(url, status)
{
  if (status == 999)
  {
      alert("You must restart your browser to complete the mySample
installation.");
  }
else if (status == -202)
       {
          alert("Access denied. You dont have permission for
installation!");
        }
}// end

The code above causes following error (see Java-Script Console):
--------------------------------------------
Error: Can't convert Error to string
--------------------------------------------
Error: error is not defined
--------------------------------------------

What's going wrong ?? I think it's helpfull to notice the user if the
xpinstall installation failed or was successfull.

I tested it on Netscape 7.1, Mozilla 1.7, Firefox 0.8. All the same
behaviour.

Thanks...

-stefan