Hi,

In conjunction with interop using MsiSetExternalUI and MsiSetInternalUI to
create a custom UI for software installation, I have declared (in a wrapper
class 'MsiInterop') the following interop signature to MsiInstallProduct:

   [DllImport("msi.dll", CharSet = CharSet.Auto)]
   extern static public MsiError MsiInstallProduct(string product, string
commandLine);

But when I call the method, I get a System.NullReferenceException.  The
offending line is:

uint err = MsiInterop.MsiInstallProduct(<<path>>, null);

Any insight would be most welcome.

--    Ian