The BBC has apologised after media regulator Ofcom found it in breach of rules over a TV competition offering a visit from the pop group McFly.
McFly were only able to visit a school within Greater Manchester
The competition was being run for primary schools by BBC North West Tonight with the charity Comic Relief.
The prize was offered across the region but on the last day it was discovered that McFly would only be able to visit a school within Greater Manchester.
The BBC "apologised unreservedly" for not telling schools this was the case.
The decision meant that a number of schools which entered the competition, held in February 2007, were no longer able to win it.
The BBC told Ofcom that it had a number of options. It could either cancel the competition, openly explain the problem to viewers or privately exclude schools outside Greater Manchester.
Producers decided on the latter option but have pointed out that the winning school was the best entrant.
The BBC accepted the process was unfair.
In its ruling, Ofcom agreed the competition was unfair because some schools had no chance of winning. It judged producers should have made the situation clear before the closing date.
Ofcom accepted there was limited harm because entry was free and the best school won.
But the regulator ruled that in future viewers must be informed as soon as possible.