True if the add-in is installed. Read/write Boolean.
Remarks
Setting this property to True installs the add-in and calls its Auto_Add functions. Setting this property to False removes the add-in and calls its Auto_Remove functions.
Example
This example uses a message box to display the installation status of the Solver add-in.
Set a = AddIns("Solver Add-In")
If a.Installed = True Then
MsgBox "The Solver add-in is installed"
Else
MsgBox "The Solver add-in is not installed"
End If