I can give you the recipe I use, I don't think your recipe had enough sugar perhaps?
8oz egg whites
1.5 cups granulated sugar (12oz)
1lb unsalted butter. room temperature, cut into pieces
whisk egg whites and sugar in a glass or stainless steel bowl over a pot of boiling water(don't let it touch the boiling water) until white feel warm to the touch (110F) and no grain of sugar can be felt.
pour mixture in a mixer bowl, using a whisk beat on high until back to room temperature. When meringue is fluffy, thorw in the room temperature butter, pieces at a time.
keep whisking until silky.
If it's too cottage cheese like, keep beating, it will come together.
If icing looks soupy, the butter was added too soon. cool the bowl down while mixing by holding an ice bag to the side.