Music system won't accept code to restart after changing battery

Hi, I have a 54 reg Clio Expression & had to replace the battery recently. Obv I needed to re-engage the sound system & found the code & instructions how to input it in my maintenance booklet. However, when I put in the 4 digit code, it looked like it had accepted it & when I pressed the number to confirm it beeped like it was sposed to - but the 4th number then kept flashing, like it still needed inputting :/ I tried a few times & just ended up getting an "Error" msg on display. Tried ringing nearest Renault dealer & they said it sounded like a software prob & to book it in, but they were wanting to charge a full service price of £99+vat!! So just wondered if anyone on here's had the same thing? I scrolled thru the 400+ posts but no-one seems to have had the same prob, they just didn't know bout needing to put the code in. Any help will be greatly appreciated, as I'm going away next weekend & will be v boring driving without my music on! Thanks a lot, Fay. :)