TRANS.FAILSAFE-can be driven in this mode for how long?

[omodos]

Greetings to all and sorry for posting this, scanned all the threads and tad above my head , to be frank not seen anyone post the same run up i had to the trans.failsafe.prog error on dash that puts the X5 into limp mode...ok its a 3.0d not sure how it differs from a petrol model but any tips greatly appreciated.

Bit of history in life of car I have gotten the error either
a. after very long drives (not always), then just switched off engine startup and all good again. and also when going down steep roads. Again error goes after stopping and starting.
b. more recently last 2 days been consistently getting messages when going down steep inclines and message again goes on stop and start engine, until yesterday where it would come on continuously.

I have stuck it on the ctek charger as in the past have had odd things happened due to low voltage but the battery is 2 months old. I know a capable mechanic but sure bet he is booked for at least 14 days, so question is can the car be driven school runs etc max 10-15 miles a day in limpmode without damage? and the other thing on passing could it be the transmission fluid specially seeing as was getting it quite consistently on downwards steep road? again appreciate any feedback...