Solved

Driver will not train weight

This is because you have already maximised all of the trainable attributes (everything except Talent and Experience) so you will never be able to make this driver any lighter.

The most effective way to develop any driver is to train Physical attributes first until stamina is 20 and weight is minimum (51 kg male and 46 kg female) before focussing on the Driving and Mental attributes. THere are two reasons for this
1) Training Physical attributes has minmal effect on level which makes training faster.
2) As you've found out, if you train everyting else you can no longer reduce a driver's weight.

Edits:
Posting at the same time as Mike.
Also I have edited your post Tim to make the driver link a hyperlink

Tim
As this is not a bug I have set the status of this thread to solved.
Kev.