Try/Catch changes the scope, so you did not see the object outside it. Do this way:

XceedZipLib.XceedZipClass loZipper
try
{
    loZipper = new XceedZipLib.XceedZipClass();
}
catch
{
    MessageBox.Show("Please check to make sure you have the Xceed Zip Compression Library installed",
		"Error: Missing Required Files", MessageBoxButtons.OK, MessageBoxIcon.Stop);

    return false;
}

loZipper.PreservePaths = false;
loZipper.FilesToProcess = ...