Buds can drop for any number of reasons, from an unwelcome change in watering (surplus or drought), a change in light, or simply being touched or moved. For example, my carnosa was building up another wave of blossoms before they started construction on my rear deck and boarded up the window it was next to. With the reduction in light, it allowed the buds to shrivel. Perhaps, if you moved it from south to north while it was budding, that was the cause.

If it is happy in the new location, it will start putting out new buds again, in a few weeks to a month. If it doesn't, you might want to consider putting it back in the south window.

Good luck!

Thanks greedy ghost, it may be my watering habits. I shall keep an eye and see how it goes in a north window