Oh, by the way, that first error about member functions on non-objects is about the weight_unit field. The importer is expecting it now for some reason, but it's not in your XML.

The rest of them are because it expects the <categories>, <manufacturers>, <classes>, and <attributes> tags, even if they're empty. This is one of those things that I need to fix, and I'm not sure there's anything you can do in the mean time except import all of those pieces of data.