SOLVED: “Invalid security token” Error In Comments on a WordPress Site

Askimet antispam had been doing a good job for us but the pricing model just did not make sense so we changed to AntiSpam Bee.  I thought all was going well but found I had no comments after 2 weeks.  We usually get several per day, so I knew something was wrong.

It turns out that AntiSpam Bee and Jet Pack are incompatible:

Antispam Bee and Jet Pack comments doesn’t appear to play nice with each other sometimes. Jetpack (among other things) makes the comment section of the website nice. However AntiSpam Bee eliminates spam and IMO one of the better ones. You can turn off the Jetpack part for the comment section if needed. Go to Jetpack -> Setting and look for ‘JetPack Comments’ – deactivate. When this is done the rest of Jetpack remain in force like analytics and other necessary items, Antispam bee works and you can leave comments – this is not ideal.
SOURCE

In our case, we gave up, uninstalled AntiSpam Bee then installed STOP SPAMMERS by Bryan Hadaway .  We have never heard of before but the plugin is:

• free
• popular with >50,000 installs
• has no required configuration

It seems to work.