Directions: Identify which part of the given sentence contains a grammatical error. The project staff are working on the weekend so as not to delay the project any further.

Step-by-step solution

The error lies in the second part of the sentence. In British English, the correct preposition to use with the word weekend is at or over. The preposition on is primarily used in American English. Therefore, the phrase working on the weekend should be corrected to working at the weekend or working over the weekend.