Cado wall unit key  

Hmm.
Judging from the photo, it's a skeleton key.
I hoard skeleton keys just for this purpose, and have found that one of my arsenal of 30-40 keys will usually fit any such lock. Know anybody with a bunch of skeleton keys?
You could take the cabinet piece to a good locksmith, and he could probably figure out which key you need, and make a duplicate.
(I have a Cado system, but no locking cabinets.)
(PS--I've dealt with large Cado systems that had multiple locking cabinets-- as I recall the same key fit each lock, if that's what you're asking).

it's easy.
look inside the lock keyhole.
If you see a small pin pertruding from the left towards the top of the key hole = No 2 key from skeleton keys 1-9.
If the pin is pertruding from the left but towards the bottom of the key hole = No 4 key.
If there are NO pin sticking out from the left or right then you are in trouble as it will be a coded skeleton key which has several teeth cut at different lenghts. Each tooth lifts a small spring loaded plate in sequenze until there is enough room for the flat face of the key to push the lock plate back.
If you have other cabinets which are not locked take the lock out and you will find a number embossed on the side of the lock/ number = key code.
If you had or can find a list / diagram of the skeleton keys 1-9 then you are in business!!
Carl F in denmark USED to sell the range in bags of 100 but have now ceased selling them.
if all else fails slide 2 thin pieces of metal into the crack between cabinet and door and gently wedge up until the lock is free. May cause cabinet damage if done with frustration!
good luck

To open without a key,
you might also try a credit card/ plastic square cut from a liter soda bottle, wedged into lock. (Though, an open door that won't stay closed isn't the ideal solution!)

Got it!
The first one anyway...
the other is resisting.
I was hoping for a white interior. : )
Now for my next trick. I'm setting up a jig to make some more uprights.
It came with 6 wall panels that don't really work. I can only use three...
Thanks for the support! When simon said 'easy', i went at it again and
without damage. And after a good nights sleep.
I was hoping for a bottle of scotch reward inside but it is pretty minty..

Mamoth lock
they are VERY basi and you should be able to open it with a flat face key.
I have only ONCE been rewarded with a bottle of booze in a locked cupboard.

Cado wall system - walnut or rosewood
Do you have any shelves and brackets you would like to sell?