I have just started using the WebSite Auditor and have optimised my page for my particular keyword but don't understand how the Bold Text Blocks element works. All my optimisations are in the green except for this which is red 17.6%. I have put my keyword in bold font so why is the rate so low?

Please take a look at the text near that table, whether it says to decrease the amount of keywords in bold. You might be over-optimized. Or you could just submit this question to http://link-assistant.com/support providing your site's URL and we'll help you out.