Ceiling Hell - Help!

Hi All,
I would like to share with you my painting nightmare. After recently having had skimmed my ceiling I thought I would get on with the easy task of emulsioning it.... but how wrong I was. I read somewhere on this site that PVA can be added to the emulsion to act as a primer, so I used this method and this primer coat went on with no trouble.
But when it came to putting the second coat of emulsion with a roller I noticed the first coat peeling off and depositing flakes of paint right before my eyes....Ahhhhhhhhh!!!!!!!
Does anyone no why this might of happened ? I made sure I left the first coat was dry ( 12 hours ).
Could it be the paint I was using which was B&Q's stuff ?
After I noticed the paint peeling off I ran my scraper and found the paint coming off easily. The ceiling now looks like a patchwork quilt of white and brown plaster, I almost took the scraper to ceiling to take the whole lot off but in the end just chose to leave it up there.
Could someone recommend what my next move should be ?
Cheers.

How long had the ceiling been plastered for before you painted it?

I know you are supposed to water down the first coat as the plaster sucks the moisture out of the paint before it can dry at its own 'pace' this means that the paint does not adhere to the plaster correctly (it dried to quickly) and it will flake off as you described

Antwerpman is bang on.
If you have got the loose stuff off, I would try a next coat watered down correctly, and applied slowly and gently- if you roller quickly, it tends to pull the paint off worse than if you go slow. I've been there too!
sometimes you have to persevere on a patch - more loose may come off on the roller, and you may have to pick it off the roller.
Then, after proper drying, do the undiluted top coat.

Pie

let it dry out fully first. use a fine filler and fill any bare areas, especially around the flakey edges. Once fully dry, lightly sand then gently emulsion over at the edges using a brush. let it dry again fully. Once its all hunky dory and looks like a smooth surface use a good quality well loaded roller and slowly roller it. Dont be stingy with the paint. let it dry fully, then a bit more before the next coat!
Usea a decent quality paint as well
Thermo