Invalid request

Could you try to deactivate Jetpack, and then delete the plugin from the Plugins menu in your dashboard? Once you’ve done so, try to install the plugin again from scratch.

If that doesn’t help, can you please use Jetpack’s Debugger module to send us some more information about your site?

1) Go to the Jetpack page in your dashboard.
2) Click on the Debug link appearing at the bottom of the page.
3) Click the link that says “click here to contact Jetpack support.”
4) Fill in the description box and your name and email address.
5) Click the “Contact Support” button.

Thanks!