Electrics: 2003 Xc90 computer problem

[Jcpearn]

hi, this is my first time asking questions, so please bear with me. what l want to know is....is it possible for someone to alter the computer on an Xc90. as my local garage says he cannot reset the computer after the service message came on.
l am currently in a dispute with the trader l bought the vehicle from as it was sold to me in an unroadworthy condition, which l found out after taking it for a service when the computer was telling me it required a service. my garage told me there maybe a problem with the electrics. any help or advice will be gratefully appreciated. l spoke with the previous owner of the vehicle,who took it back to the trader when the engine management light came on after having the vehicle for just over a week. they swapped the vehicle for another one, then l came along 2 months later and bought it. is it possible to tamper with the computer..?

[cheshired5]

What is the exact wording of the message?