Errata

errata is a plural word. (Originally this was Latin. It means ‘mistakes’, and is used mostly as the name for a list of misprints in a published book.) The singular form is erratum. (In Latin, the regular plural of nouns ending in –um was –a.)

Therefore it is a mistake to talk of ‘one errata’. It is ‘one erratum’. This is the sort of thing that academics like to comment on – when they know it.