A4 Wont accept key

[Una]

When i put my fob key into the ignition of my A4 TDi the orange light on the dash flashes and it wont let me start the engine, this has happened before several times and i was adivised to give the key a rub to clean it, but this time it happened was several hours ago and it still wont work, any ideas.

[Ben]

does your spare key work?

If so it cant be the immo.

It could be the battery in the fob.

[Una]

yes its happening with both keys, the second key is a copy and has no pob but we cant remember the last time the key battery's were changed, so we'll do that, i was reading a post lower down that was saying that it could be something in the exhauste or a coil in the ignition damaged by moving the streering column, another mentioned using a spray called servisol in the key hole that it solved his problems so we will start working our way through these and if needed get it to a audi garage

[ini]

If the reader coil for the immobiliser has a bad connection, try moving the adjustable steering column 'up & down' and 'in & out' a little.

If it works again after doing this, the immob coil is most likely defective.

[Una]

Eventually got the car going, took it to an audi dealer, they put it on the computer, turns out that the key had to be recoded, now working perfectly, thanks everyone for your help