La oración correcta es "Debo realizar mi trabajo". <u>This means that I must do my job</u>. It's an obligation, that's what the verb "deber" implies. It's used in Spanish as "must" is used in English. The other sentence, "Debo realizar mi error", makes no sense. In English it means "I must make my mistake", as if making a mistake was my obligation which is incoherent.
