This error message occurs:
<ConditionData> Validation Failure: Site Id is wrong </ConditionData>
The wrong DHL configuration has been enabled in Magento.
Use the correct configuration section for the DHL extension. It is located here:
When using the DHL extension, make sure not to enable any other DHL configuration in Magento. If you do this, you are enabling the DHL integration for the USA, which is not compatible with DHL Germany.