help!?

this problem has occured 4 times now and is becoming a hassle as i keep getting stuck in the worst places, i have a 1.2litre 8V renault clio authentique '51 plate, my car will turn as normal and run perfectly for around 5 minutes at which point the immobilizer light will appear and the throttle and clutch will stop working, the car is still ticking over as normal but there is no power in the throttle or clutch so cannot even move on the bite point. on two occasions i have turned the car off, left it for around 5-10 minutes and turned it back on and the problem seems to have solved itself. on the occasions when it hasnt it has been taken into the garage and tested but no probelm could be found, the engine was cleaned and still no problems. each time this problem has occured it has been raining at the time or has rained beforehand, the mechanics at the garage even went to the lengths of throwing water over the car and testing it and found nothing wrong but it seems more than a coincidence to me! please help...