'07 Fiesta Zs Tdci Help

Evening all. My missus' Fiesta went in for a cam-belt change and it's not come back :(

Now, I'm going to try and simplify what I understand to be happening, so I may be a little off with some technical terms and some info if there are any questions!

My mate owns the garage and currently doing the work. From what he has said, he has timed everything up as per the system they use, put it all back together but every time he attempts to set it all by hand, the cam-chain slips or jumps a tooth. He says he has checked all the tensioners etc and all seems normal. (he said normal as he has done several of these and done the cam-belt on my Fabia vRS literally the day before)

Naturally, he had stripped everything down, put back together to try and eliminate things, but the cam chain keeps jumping off the wheel?

Currently, we have the cams out..... He's lined up the cam chain, the wheels they are on, the cam wheel etc obviously put back together and as he's attempting to do the full cycles he needs to do but part way through these cycles the cam chain slips or jumps off/out the teeth. When I was round there last night the cam tray or cam holder? (below pic) was on his bench and showed me how it all lined up, explained how the rest of it gets timed. He showed me the many revolutions that the chain needed to do to get the marked teeth of the wheel to line up with the white indicators on the chain itself to show me there was no probs this end, but can't understand why it slips the chain or whatever it does inside once back together back on the engine block when trying to complete the cycles to complete the timing?

The head is meant to be coming off this evening to see if there is anything obvious in there, but he's not expecting there to be anything, but surely there must be if everything else is ok?!

Sorry for the brain dump, but the car has been in his garage since December (been working on it between jobs so not to charge me above the normal cam-belt charge) and my missus is now starting to panic as she only bought it 2 weeks before it went into the garage.... private sale so no fall back :(