Older versions of Sol Free were included for free in several software bundles and book CD-ROMs. These versions did not include the Sol Manual in the distribution, which is why you are getting this message.
Unless you prefer the older software, you should download and install the latest version of Sol Free. The software is greatly improved over the older version you have now and the manual is included. Sol Free is a free download.
If you want to keep the older version of Sol Free, the older Sol Manual is still available for download.