Global Radio management found that only the first entry, of people who entered a number of times using the same mobile phone, was counted.
Media regulator Ofcom said that the fault emerged, after a listener who sent multiple entries contacted the station, saying he did not win despite his high number of entries.
The company tried to rectify the error by re-entering those texts which were mistakenly excluded into additional draws. Ofcom welcomed the broadcaster's action in uncovering the problem and cleared it of any breach of broadcasting rules.
In a related development, Global Radio's 95.8 Capital FM station has signed the R&B star Akon to present a weekly Saturday evening show between 7pm and 9pm.