Grave errors of the East' refers to the criticisation of Orientalists by other English officials.
In the early 19th century, many British officials criticised the orientalist view of learning. They believed Eastern knowledge was full of errors (mistakes) and unscientific thoughts, and it focused more on non-serious literature.
James Mill criticised Orientalists and argued for emphasising practical and useful education, like scientific and technical advances of the West.
By the 1830s, Thomas Babington Macaulay strongly criticised Orientalists. He viewed India as uncivilised and advocated for teaching English language to civilise the people.