It's probably what is called "damping off" that is your problem.

If you look up the term in here or Google it you should find all you need to know regarding the problem--it is a fairly universal one when growing from seed.

Probably you are keeping them too wet. That is when damping off hits. It doesn't need to be 'fairly universal'. I've not had problems with it. It's all down to the watering.

Thanks for bot responses, sincemy last batch died again I am going to try both ideas in diferent pots. hopefully at least on works :)