The Jolly Boys' Outing - S6-E7
Continuity mistake: In 'The Unlucky Winner Is' (which is set before Rodney and Cassandra marry) Del changes Rodney's date of birth to 2nd November 1974 in order to make him appear 14, meaning this episode is set sometime between November 1988 and November 1989. However, in this episode, which takes place after Rodney and Cassandra have been married a whole year, a sign in the window of the coach (which can be seen just as the coach is leaving the police station) states that this episode takes place in 1989, and it is on a Bank Holiday weekend, thus can be no later than August 1989.
Chosen answer: An apparent long string of illnesses.