Unable to get the Add propert of the addin class

[jayklmno]

I am trying to uninstall an old addin and install teh new version by having
the user open a workbook. The code I am using is as follows:

Sub Install_Grid_addin()

Dim oAddin As Object

If AddIns("Grid_Addin").Installed = True Then
AddIns("Grid_Addin").Installed = False
End If

Set oAddin = AddIns.Add("\\networkpathtofile\Grid_addin.xla", True)
oAddin.Installed = True

MsgBox "Installed!", vbExclamation

End Sub

It continuously generates a "Unable to get the Add property of the addins
class."

What might be the error or is there a better way?