I took a look and sure enough the site’s robots.txt file was set up to block Google and the other search engines from crawling the entire site. Fortunately the fix was easy. I changed the file from this:
User-agent: *
Disallow: /
To this:
User-agent: *
Disallow:
Problem solved.
(You can also just remove the file.)

I might be going out on a limb here, but I’ve seen more problems caused by misuse of the robots.txt file than solved.

One of the big misconceptions about robots.txt disallow directives is that they are a fool proof way to keep pages out of the Google index. Not only is this not true, but when the pages are indexed – they are indexed with almost no information adding a lot of low quality almost duplicate content into the index which might drag down the SEO performance of your site.

The robots.txt file has been around for years. In those early days, bandwidth was more precious and Googlebot often taxed servers, even crashing them, when it crawled a site. So using the disallow directive to keep Google from crawling pages often helped keep a site up. Those concerns are a distant memory today.