Magento - Blank page when trying to add new SOAP/XML-RPC role

Hi,

We often see the following problem when trying to install a new Magento extension:

After installing the extension/module on Magento 1.8, when trying to add a new SOAP/XML-RPC role I get an empty blank page.

This shows up in the http log:

PHP Fatal error: Class 'Remarkety_Mgconnector_Helper_Data' not found in /var/www/html/app/Mage.php on line 547, referer:
.../index.php/admin_url/api_role/index/key/...

What to do when this happens?

1. Clear Magneto cache
2. Run Compilation Process (re-compile)

Cleaning cache through the Magento Admin Panel

1. Log in to your Admin Panel account
2. Go to the System -> Cache Management section
3. Click on the Flush Magento Cache button

Run Compilation through the Magento Admin Panel

1. Log in to your Admin Panel account
2. Go to System > Tools > Compilation and click on 'Run Compilation Process' to re-compile Magento
3. Enable it again by clicking on 'Enable'.

Thanks,