Auto transmission problems

Hi guys
I have recently bought a 02 td5 disco auto and given it a full service including the transmission, before the service the transmission was selecting a high gear on start off and the m&s lights were flashing,this was happening in any position on the selector and if the transmission was hot or cold. The system could be reset by switching off and on the engine.
I drained the auto fluid , changed filter and filled oil with engine running and selector in neutral through filler point on front of sump. All has gone well for the past week or so since service, weather had been dry but has now turned very wet and old problem has returned. Anyone got any ideas maybe possible electrical fault or weather is just a coincidence.

cheers for help

Can't be sure about your model but my oil level should be checked with a cold engine. My garage obviously did it while the engine was hot so when I checked it one cold morning the levels were off the stick. Its surprising how much difference the temperature can make to the levels.