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

GetShipmentData: Request contains an unsupported character


Order or order item details need to be verified and checked so that no unsupported symbols or characters are present in item's data, title, description or in the extended property values for HS Tariff Code and Country Of Origin. 

Typically the unsupported symbols or characters will consist of double quotes, irregular question mark signs etc.