This message indicates that a critical error has occurred while executing the installation script. The iDEAL Checkout framework has created an error log for this, which you can find at the following location: ../idealcheckout/temp/
The error often means that the database configuration is incorrect. Our advice is to check this configuration (../idealcheckout/configuration/database.php). Most likely, the installation will need to be performed again after adjusting the database.php file.
If you cannot find the database information for your webshop, you can contact your hosting provider. They can provide you with the necessary data.