Firstly shut down scrapebox. Then go into your main scrapebox folder, then into the configuration folder, then edit scrapebox.ini.
Under the [Advanced] section, find this line
0 on the end means its disabled, to use proxies change it to 1, so it would be
Then SAVE the ini file, and then launch scrapebox.
If you do not have that line in your ini, then you can add it under the [Advanced] section, or just update scrapebox by downloading the latest package, found here:
You can download scrapebox from here:
This will force scrapebox to use proxies with the keyword harvester. Generally you don't need proxies as most places will not ban your IP, but bear in mind if you add in non working proxies into scrapebox, the keyword scraper won't work either.