Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
mĭnistĕrĭālis, e, adj. [ministerium], ministering (late Lat.): spiritus, Rufin. Orig. Princip. 1, 5, 1.
Hence, mĭnistĕrĭāles, ĭum, m., imperial officers, Cod. Th. 8, 7, 5 al.