Unable to install/load xll addin via vb.net

[Rich Russell]

I have an xll addin that runs in Excel when it is loaded via the Excel menus. 

However, I get an error if I attempt to install it programmatically (VB.NET).   

System.Runtime.InteropServices.COMException
  HResult=0x800A03EC
  Message=Unable to set the Installed property of the AddIn class
  Source=mscorlib

Here's a brief snippet of the code:

For Each AdnX As AddIn In AppEve.AddIns2    ' complete list of addins collection

      If "g:\addins\myaddin.xll" = AdnX.FullName and not adnx.installed) Then
                adnx.installed = True
      endif

next adnx 

The error occurs at the line in RED.

Thanks for any help.

Rich