Unfortunately, at this stage, the DPD and bpost module both load a Google maps api, DPD loads later (comes later in alphabet) so overwrites the bpost gmapsapi code breaking the module.This is not a bug neither on bpost nor DPD module but let's say an integration issue.

You would like to work with both bpost and DPD on your Magento Webshop ?

Don't worry, a workaround has already been developed. Please visit

https://github.com/DPDBeNeLux/magento-DPD_Shipping/issues/49#issuecomment-187133239

 for more technical informations.