E39 Driver Door lock problem

Hi All,

My year 2000 528ias has developed an intermittant problem with the
central locking.

When clicking the unlock button all doors but the driver's door unlock.
It will not unlock when you use the key.
It will not unlock when you get in through the passanger door and press
the unlock button on the centre console.
When you lean over from the passangers side and pull the handle on the
inside of the drivers door the "pin" on the door pops up then down
again and the door still won't open.

The only way into the drivers seat when this problem occurs is to climb
across the passanger seat - at 6"3 and 18 stone this is less than
elegant...

After driving for a mile or two I press the button in the console again
and the door unlocks.

Your help would be greatly appreciated.

Cheers

Ralph