B757 Captain reported Oxidize 5.1 ADG (Accessible Dangerous Goods) ULD was incorrectly loaded onto an IDG (Inaccessible Dangerous Goods) ULD Unit Load Device during preflight. Ultimately the Oxidizer was removed to be correctly loaded onto an ADG ULD on a subsequent flight.

Narrative

On presentation of the DG staff; FO noted that the manifest was not correct to what was being shown. An ADG (Accessible Dangerous Good) and IDG (Inaccessible Dangerous Goods) ULD (Unit Load Device) were shown. The manifest showed that an ADG but the second page of the DG staff paperwork had it stowed in the IDG ULD. The FO brought this to my attention and to my understanding; I believed this was not possible. I consulted the DG staff job aid and confirmed that the class is ADG. I then called the Duty Officer to confirm my belief that if it was labeled as ADG and that it had to be in an ADG ULD and manifested as such. The ZZZZ ramp told us that this is the way they have done it for many years. I then called the DG Duty officer to verify which was the right course of action. The DG staff officer got a supervisor on the line and told us that it is ADG; it had to be loaded into an ADG only ULD. The ramp was informed of this and I had them remove the Oxidizer 5.1 and roll it into another flight. Upon landing in ZZZZ1; I contacted the DG staff officer for further info concerning this info and she again confirmed that the ADG had to be loaded into an ADG only ULD. I have never run into this scenario before but the ramp was adamant that we were incorrect.Cause: I believe that the manifest was done in error and that the ramp incorrectly loaded the ADG into the IDG ULD.Suggestions: A more thorough explanation of the ADG and IDG classes of materials; and the standards for loading them.