Just a quick post it's not really a guide but it may help a few as this problem seems pretty common.
When unlocking the car with your fob, in my case all doors open bar the driver (typical).
If the key is then used to unlock the drivers door it then opens.
It doesn't happen all the time mainly if the car has sat for a few hours locked. The car will always open from the inside.
I tried replacing the control module (little black box which controls most electrics in the door) as vcds pointed to this but it wasn't actually the problem because shortlydown the line it started again.
So I stripped the door down to get access to the mechanicals of the lock.
You need to remove the exterior door handle, door panel and a smaller inner panel. All quite simple to remove and guides can be found easily.
Once you have the lock out (take car not to kink either of the two cables!) it should look like this, in the picture that is the operating cable for the exterior handle.
Remove the grey cover to expose the lock mechanicals as so.
You should see the that the grease applied from factory has clunked/dried up. I thoroughly cleaned the unit and re greased all mechanicals
Touch wood, so far I haven't been shown up and got my key out to open my 2008MY car lol
Hope this helps