Thanks Daniel for your considered reply. My web host (eventually) enabled error logging and you were spot on - IonCube needs to be upgraded:
PHP Fatal error: The file xxx/modules/addons/solutedns/solutedns.php cannot be decoded by this version of the ionCube Loader.

Hi guys, After i install 0.2.2 into /modules/addons and then navigate to Setup > Addon Modules in the WHMCS admin UI, I get error 500 server error. Removing the solutedns folder returns things back to normal. Has anyone else experienced this? Unfortunately my web hosting provider has disabled error ...