=Why AddIns.Installed can be out of range=
 

I am trying to verify if the Analysis Tollpak is installed with the following
sentence:

If AddIns("Analysis ToolPak").Installed = False Then
MsgBox "Analysis ToolPak is not installed"
End If

The problem is that I receive a error when I run this code. In the first
line, VBA stops telling me "Subindex out of interval", making reference to
the string argument.
If I replace the argument of the AddIns property by for example an 1, I
don´t receive the error box. It works!!. However, if you check the online
help there are many examples where the AddIns property can accept strings and
numbers as argument.
Where I am making the error?