Thijs Leuven said:Any clue what this could be? Have to say that I haven't checked the gearbox oil in ages, might it just be a low oil level?
Checking the gearbox oil level is so easy it would be foolish not to check it first, but it's more likely to be a problem with the selector linkage, and most likely the selector striker lever having over-ridden the selectors on the box.
You should be able to see whether that's the case by looking up from underneath, or possibly through the access hole in the tunnel for the reverse light switch.