Hi Paul,
As 7403406 suggests, your car is
probably complaining of a lack of Eolys additive for the diesel particle filter, (FAP), in the exhaust. I say probably, because I think the error message should be 'Minimum level diesel additive', or something similar - not exactly sure as I've only seen it once on a car I was thinking of buying. It also had the particle filter blocked warning light on, but the handbook didn't describe it correctly. (this car was an 02 reg GTX).
If that's your problem, you need the tank refilled, and the counters in the additive ECU reset, for which the stealers tend to charge about £170 AFAIK. You can't simply top it up, with out the counters reset, the fault will still be there. Best not to leave it - there is a body of opinion which suggests the low level sensor in the additive tank will fail if left empty.
Have a look at
this for a fuller explanation
