In the case of an incomplete download, the problem isn't with the model itself; rather, the failed download results in an incomplete file that SketchUp can't recognize or open.
Incomplete downloads can be caused by many different things, for example, heavy Internet traffic, transmission errors, and slow connections (some dial-up services might not be able to handle large file downloads). You may notice that the download process simply stops before the entire file has been downloaded, or you may see an "Unexpected File Format" or "File not found or invalid" error at the end of the download.
In cases like this, you still may be able to successfully download the model; however, before you try the download again, it's important to clear yo clear your browser's cache.
It may also help if you try the download at a later time when Internet traffic is not so busy, and to save the model to your hard drive rather than loading it directly into your SketchUp model.