ive recently bought a 2009 audi a3 , and the central locking worked fine
with the fob, then a few days later , it wouldnt open the driver door
unless i unlocked with the key

and if you do the 2 click on the remote to open all doors , it unlocks all but the driver door !
the fob remote , locks it all up , with no problem
any advise please

Could be the door control module similar to this:

 

http://www.ebay.com/itm/181248982631

 

That one is off an A4 but I have heard of other people having issues with these

ive no idea , ive been told , to spray some WD40 into the lock as it  could be sticking ,  so im gonna give that a go ,

but thanks , for the help