Can someone advise me on this?

My wife has a peugeot 206 1.4 auto (x reg). Occasionaly when driving you hear a clunk in the car & the sports mode light & the ice warning light flash alternately. The car then sticks in 3rd gear. We took it to an auto gearbox specialist who told us the solenoid had gone (a common fault apparently). He replaced the solenoid, but 3 days later the car did the same thing. we have had it back to the gearbox specialist & to a peugeot main dealer, but no one can tell us what's wrong other than it may be an electrical fault like a loose connection somewhere & it's just a matter of trying different things to eliminate the problem. I have had it to the local garage for MOT today, which it passed. While I was there I quizzed the mechanic about the problem. He has run a diagnostic check on the gearbox & said that it has come up with 2 fault codes: (33) Torque reduction & (39) Accelarator pedal position sensor. Although he did say that the gearbox was recognising the accelerator & it appeared to be working as it should. He also ran a diagnostic check on the engine management system which returned no faults. If anyone out there can give me some advice on how to cure this problem I would greatly appreciate it. I have spent £300 so far on trying to sort the car out & it's no different to what it was £300 ago. I just don't want to spend any more money on something that's not going to make any difference. My local mechanic suggested that I post this on the 206 owners club forum, as he had had valuble information in the past form owners club members. If anyone has had a similar experience with thier car, or can offer some advice on this problem could you please point me in the right direction. Many thanks.