The mention of the MXM file is normal and is not a problem, it just means that the MXM was not found at the path specified, but was found using search paths.
Regarding the TextureWriter, in general, the main effect of the TextureWriter failing to write all textures will be a slowdown of the export, since the plugin must then ask SketchUp to write each texture individually. A valid question is why it failed: it could be due to a specific problematic texture in the model, but it is hard to say; this failure is a common one on the OSX side, and I've never seen a real reason for it in that case.
One thing you might do is to update to version 2.7.10 of the plugin, available for download
here. There are not huge changes, but it would not be a bad idea to update. Lastly, you might try to isolate the problem by hiding half of the model, trying to render, and if it still fails, hiding half of the remaining model -- and so on. One can usually narrow down a problem pretty quickly using this method.