How are you creating the PDB file? PDB is a container which can hold a number of different formats. What type of PDB does Ingram want? If it's an eReader formatted PDB then anything you create with
Dropbook will be valid. There is no validator tool for eReader formatted PDB files because the format is proprietary. If you are creating an eReader PDB file with
calibre than that may not work because it does not produce 100% perfect files. It just produces ones that will work with the desktop software (I'm told there are issues with some reading on some mobile versions of the software).