I am not able to reproduce this -- is it any particular texture, or type of texture that is missing, or any other type of file (i.e. MXM)?
When you use Studio to open a pack-and-go MXS that was written with the plugin, you should find that all of the textures have been given relative paths, pointing to the /textures folder, which is created next to the MXS file. This means that unless a missing texture can be found by Studio at one of the search paths set in Studio Preferences, it should be missing when you render that MXS from Studio, or in Maxwell Render.
The only way I can think for a texture to be missing, would be if SketchUp could not write it to disk correctly during export. So perhaps if you can send me the file, I can try to reproduce it here. You could upload it somewhere, and post a link, or if you can reproduce it using a small enough file, you could send it to my email, which should be listed below.
Next Limit Team