Solicitor won't exchange/complete Builder withdraws sales contract

[SimpleStu]

Help,
Anybody in this situation- I'm in a desperate state about my new build home sale seemingly falling through hours before exchange and week before completion.
I saw an off plan property for a large development in Jan. and have watched it being built during phase 2 out of 3.
originally builders wanted a 5 week exchange- not possible because no brick laid until March.
Start of June I went for the final inspection, letter saying exchange 25th, complete 30th June.
25th June- solicitor said no, there are conditions which have not been discharged.
Builders have now withdrawn contract, but other people have moved into neighbouring properties.
I had mortgage, nothing to sell, and was waiting for the house to be built.
I don't understand if others can move in, my solicitor says no, builder has put my house back on market (although it has all my specified optional extras)
Any ideas what are these non-discharged conditions, that could be so serious I can't proceed?
Any advice to get this back on track will be gratefully received, but I'm fearing I've lost this house.
Good luck with your own situation- I'm discovering it's so bleeding difficult.
ps. the house is quality finish and build quality so no issues there, I want the house.