Strange goings on like you describe are often down to something simple like a wire disconnected. Check inside the boot area for any possible connections to the rear light clusters that may have been disturbed. Has someone accessed the spare wheel or the storage compartments on either side and perhaps dislodged a connection? Check any earth connections as well, they are easier to access and therefore easier to disturb by mistake! I very much doubt it is anything serious. Good hunting.
Richard
December 2008