Intermittent Fault

[ZPM]

A problem has started and occurred 3 times now in the space of a month. The car (2003 2.0 saloon model) has a semi automatic (selectable option) gearbox which you can drive automatically or you can select some forward drive gears overriding the sequence the car selects. When the car takes its first trip of the day, it starts out fine, drives as well as ever, yet, when we arrive at the destination and prepare to park by selecting reverse and applying a little throttle, the car behaves as if you've put it in neutral - makes a lot of revving and goes nowhere fast. Most uncharacteristic. I've had to overcome this by selecting Park and back to reverse (effective on one occasion), by changing to neutral and back to reverse (with no effect so have gone on to drive then back to reverse which worked); the last time I tried just putting it in drive and then into reverse again. It took a couple of goes but went into action.

Does anyone know whether this is a selection fault to do with the lever mechanism, or is it the automatic transmission beginning to give up on us? Has anyone else experienced an equivalent problem? If so, how was it solved - did it need expert mechanical attention or did it clear itself? Grateful to know. Thanks.