'Dancing In The Moonlight' by Toploader was the first song to be released by the band, but it didn't chart. Having released a number of other, more successful songs, the band re-released 'Dancing In The Moonlight' which took off on the fame the band had aquired in the mean time. It's possible therefore that the 'first version' you heard was the band's original - these re-releases which chart second time around are known as 'sleepers' in the music business.