Read the instructions that came with the mold again. Lube the points where suggested, clean with a solvent before use, smoke the cavities, etc. However, some people are a little heavy handed to learn to use an aluminum mold and would do better with an iron one. As much as I prefer iron molds, I cannot really say that when treated properly, the aluminum molds will not cast good bullets without problems.
Not often mentioned by Christians: Numbers 31:17-18