Vito Clutch/gearbox etc:?

Hi,
I have just removed the gearbox from my mercedes vito 110cdi and replaced the concentric slave cylinder because I couldnt select any gears. Whilst i had it out I checked the clutch and its fine, so I then replaced the gearbox and pressure bled the system, all in all it took me into the early hours of this morning laying on my back on a gravel drive with the gearbox on my chest to remove/replace, not the most ideal way of doing such a job.
Still at 1.30am I finished the job in hand, I started my vito and all was fine again, gears selecting/clutch biting well, all was good, Well until until just a few hours ago when I went to go out and once again I cant select any gears.
Ive tried re-bleeding the system to no effect.
Can anyone HELP!