I have tried printing a DHL shipping label and am seeing an error returned:

GLOBAL_MASK_ERR_002: Invalid postal code of a consignee. Please provide a valid postal code for a consignee and resubmit


Usually that error is returned if the postcode in the shipping address field is not recognized by DHL and requires some amendments. Correctness of the postcode can be checked here:  

Once checked, please amend the postcode by right clicking on the order and selecting Edit order option.