NoDictionaries   Text notes for  
... Corbulo comitatem epulasque; et rogitante rege causas, quotiens novum...

rogitante rege: this might also be an accusative as direct obj. of "adfecit": "Corbulo impressed the king, who was asking the reasons [for Roman military practices such as the four-part night watch]"; perhaps, the ablative emphasizes both the king and Corbulo. Note the alliteration.