Well, there was a significant enough bug in the previous release (rc9) that a new update was warranted so...
J!WHMCS Integrator v2.12rc10 is now available for download.
The previous release generated an "Invalid Action" when logging in from a WHMCS login form... this has been corrected. Another minor bug with the parsing mechanism involving the Shape5 template style has also been addressed and corrected.
If you are running RC9, we recommend upgrading to RC10 - if you are using a previous release you don't necessarily need to upgrade.