Complex sentence: In 2010, the contest was supposed to have taken place in Oslo, Norway, but it was cancelled due to Denmark pulling out in order to revise the participant requirements for DR's participation in the contest.
Split into simpler sentences: In 2010, the Contest was supposed to be taken place in Oslo, Norway but It was decided to be cancelled. Because Denmark had pulled out in order to revise the participant requirements for DR's participation in the contest.